diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Contracts/MTConnectTagDefinition.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Contracts/MTConnectTagDefinition.cs
index aaf040b8..d2132e14 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Contracts/MTConnectTagDefinition.cs
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Contracts/MTConnectTagDefinition.cs
@@ -26,27 +26,17 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.MTConnect;
 /// </param>
 /// <param name="MtCategory">
 ///     The DataItem's MTConnect <c>category</c> attribute — <c>SAMPLE</c>, <c>EVENT</c>, or
-///     <c>CONDITION</c>. Optional metadata carried through for browse / display; not consulted by
-///     the value-mapping path. Default <c>null</c>.
-/// </param>
-/// <param name="MtType">
-///     The DataItem's MTConnect <c>type</c> attribute (e.g. <c>POSITION</c>, <c>EXECUTION</c>).
-///     Optional metadata. Default <c>null</c>.
-/// </param>
-/// <param name="MtSubType">
-///     The DataItem's MTConnect <c>subType</c> attribute (e.g. <c>ACTUAL</c>, <c>COMMANDED</c>).
-///     Optional metadata. Default <c>null</c>.
-/// </param>
-/// <param name="Units">
-///     The DataItem's MTConnect <c>units</c> attribute (e.g. <c>MILLIMETER</c>,
-///     <c>REVOLUTION/MINUTE</c>). Optional metadata. Default <c>null</c>.
+///     <c>CONDITION</c>. Read by the write path (a CONDITION is never writable). Default <c>null</c>.
 /// </param>
+/// <remarks>
+///     Review 2026-10-21 T-3: the <c>MtType</c> / <c>MtSubType</c> / <c>Units</c> members were carried here and
+///     read by nothing — deleted. A stored blob or <c>tags[]</c> entry that still carries <c>mtType</c> /
+///     <c>mtSubType</c> / <c>units</c> keeps loading (unknown JSON keys are skipped); the AdminUI tag editor reads
+///     those keys straight off the blob for its display and type-inference advisory, not through this record.
+/// </remarks>
 public sealed record MTConnectTagDefinition(
     string FullName,
     DriverDataType DriverDataType,
     bool IsArray = false,
     int ArrayDim = 0,
-    string? MtCategory = null,
-    string? MtType = null,
-    string? MtSubType = null,
-    string? Units = null);
+    string? MtCategory = null);
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Contracts/MTConnectTagDefinitionFactory.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Contracts/MTConnectTagDefinitionFactory.cs
index 0458764b..5ff0a3ac 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Contracts/MTConnectTagDefinitionFactory.cs
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Contracts/MTConnectTagDefinitionFactory.cs
@@ -87,10 +87,7 @@ public static class MTConnectTagDefinitionFactory
             parsed,
             blob.IsArray ?? false,
             blob.ArrayDim ?? 0,
-            blob.MtCategory,
-            blob.MtType,
-            blob.MtSubType,
-            blob.Units);
+            blob.MtCategory);
 
         return true;
     }
@@ -264,11 +261,5 @@ public static class MTConnectTagDefinitionFactory
         public int? ArrayDim { get; init; }
         /// <summary>The MTConnect DataItem category.</summary>
         public string? MtCategory { get; init; }
-        /// <summary>The MTConnect DataItem type.</summary>
-        public string? MtType { get; init; }
-        /// <summary>The MTConnect DataItem sub-type.</summary>
-        public string? MtSubType { get; init; }
-        /// <summary>The engineering units, when authored.</summary>
-        public string? Units { get; init; }
     }
 }
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect/MTConnectDriver.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect/MTConnectDriver.cs
index 0440c81c..717cf2c0 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect/MTConnectDriver.cs
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect/MTConnectDriver.cs
@@ -3408,10 +3408,7 @@ public sealed partial class MTConnectDriver
                 : ParseEnum<DriverDataType>(dto.DriverDataType, dto.FullName, driverInstanceId, nameof(MTConnectTagDefinition.DriverDataType)),
             dto.IsArray ?? false,
             dto.ArrayDim ?? 0,
-            dto.MtCategory,
-            dto.MtType,
-            dto.MtSubType,
-            dto.Units);
+            dto.MtCategory);
     }
 
     // ---- v3 tag binding: RawPath ↔ dataItemId, and the definitions the index coerces against ----
@@ -3680,10 +3677,7 @@ public sealed partial class MTConnectDriver
             inferred.DataType,
             inferred.IsArray,
             (int)(inferred.ArrayDim ?? 0),
-            dataItem.Category,
-            dataItem.Type,
-            dataItem.SubType,
-            dataItem.Units);
+            dataItem.Category);
     }
 
     /// <summary>Flattens a device model into a <c>dataItemId → DataItem</c> lookup; null ⇒ empty.</summary>
@@ -3953,12 +3947,9 @@ public sealed partial class MTConnectDriver
         public int? ArrayDim { get; init; }
         /// <summary>The MTConnect DataItem category.</summary>
         public string? MtCategory { get; init; }
-        /// <summary>The MTConnect DataItem type.</summary>
-        public string? MtType { get; init; }
-        /// <summary>The MTConnect DataItem sub-type.</summary>
-        public string? MtSubType { get; init; }
-        /// <summary>The engineering units.</summary>
-        public string? Units { get; init; }
+
+        // mtType / mtSubType / units were bound here and read by nothing (review 2026-10-21 T-3); a document that
+        // still carries them parses — System.Text.Json skips unmapped members.
     }
 
     /// <summary>Background connectivity-probe knobs (consumed by the probe loop).</summary>
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect/MTConnectDtos.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect/MTConnectDtos.cs
index 9672d455..2e012d22 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect/MTConnectDtos.cs
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect/MTConnectDtos.cs
@@ -162,11 +162,6 @@ public sealed record MTConnectStreamsResult(
 ///     The observation's own <c>sampleCount</c> attribute — the number of values a <c>TIME_SERIES</c>
 ///     vector claims to carry. The index checks the parsed vector against it. <c>null</c> when absent.
 /// </param>
-/// <param name="SampleRate">
-///     The observation's own <c>sampleRate</c> attribute (samples per second) on a <c>TIME_SERIES</c>
-///     observation. Carried for the parser contract; not yet surfaced on the served node (see
-///     docs/drivers/MTConnect.md). <c>null</c> when absent.
-/// </param>
 /// <param name="Entries">
 ///     The parsed <c>&lt;Entry key="…"&gt;</c> children of a <c>DATA_SET</c> / <c>TABLE</c> observation, in
 ///     document order, or <c>null</c> when the observation had none. A <c>TABLE</c> entry carries
@@ -195,7 +190,6 @@ public sealed record MTConnectObservation(
     DateTime TimestampUtc,
     bool IsStructured = false,
     int? SampleCount = null,
-    double? SampleRate = null,
     MTConnectConditionDetail? Condition = null,
     IReadOnlyList<MTConnectDataSetEntry>? Entries = null,
     bool ResetTriggered = false,
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect/MTConnectStreamsParser.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect/MTConnectStreamsParser.cs
index 19b3df29..d2a0fc72 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect/MTConnectStreamsParser.cs
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect/MTConnectStreamsParser.cs
@@ -383,7 +383,6 @@ internal static class MTConnectStreamsParser
         var timestampUtc = default(DateTime);
         string? conditionState = null;
         int? sampleCount = null;
-        double? sampleRate = null;
         var resetTriggered = false;
         var hasCount = false;
         List<MTConnectDataSetEntry>? entries = null;
@@ -421,11 +420,6 @@ internal static class MTConnectStreamsParser
                     NumberStyles.Integer,
                     CultureInfo.InvariantCulture,
                     out var count) && count >= 0 ? count : null;
-                sampleRate = double.TryParse(
-                    MTConnectXml.OptionalAttribute(reader, "sampleRate"),
-                    NumberStyles.Float,
-                    CultureInfo.InvariantCulture,
-                    out var rate) && double.IsFinite(rate) ? rate : null;
             }
 
             // The slot is reserved BEFORE the subtree is read, and filled after: an observation is
@@ -485,7 +479,6 @@ internal static class MTConnectStreamsParser
             // away a perfectly well-determined state.
             IsStructured: !isCondition && hasElements,
             SampleCount: sampleCount,
-            SampleRate: sampleRate,
             Condition: condition,
             Entries: entries is { Count: > 0 } ? entries : null,
 
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests/MTConnectDriverOptionsTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests/MTConnectDriverOptionsTests.cs
index aa2d989f..db875d10 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests/MTConnectDriverOptionsTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests/MTConnectDriverOptionsTests.cs
@@ -95,14 +95,11 @@ public sealed class MTConnectDriverOptionsTests
         var pos = new MTConnectTagDefinition(
             FullName: "dev1_pos",
             DriverDataType: ZB.MOM.WW.OtOpcUa.Core.Abstractions.DriverDataType.Float64,
-            MtCategory: "SAMPLE",
-            MtType: "POSITION",
-            Units: "MILLIMETER");
+            MtCategory: "SAMPLE");
         var partCount = new MTConnectTagDefinition(
             FullName: "dev1_partcount",
             DriverDataType: ZB.MOM.WW.OtOpcUa.Core.Abstractions.DriverDataType.Int64,
-            MtCategory: "EVENT",
-            MtType: "PART_COUNT");
+            MtCategory: "EVENT");
 
         var o = new MTConnectDriverOptions { AgentUri = "http://agent:5000", Tags = [pos, partCount] };
 
@@ -111,25 +108,47 @@ public sealed class MTConnectDriverOptionsTests
         o.Tags[1].ShouldBe(partCount);
     }
 
-    /// <summary>MTConnectTagDefinition round-trips its positional fields, including MTConnect metadata.</summary>
+    /// <summary>MTConnectTagDefinition round-trips its positional fields, including the category the write path reads.</summary>
     [Fact]
-    public void TagDefinition_carries_dataItemId_and_mtconnect_metadata()
+    public void TagDefinition_carries_dataItemId_and_mtconnect_category()
     {
         var tag = new MTConnectTagDefinition(
             FullName: "dtop_2",
             DriverDataType: ZB.MOM.WW.OtOpcUa.Core.Abstractions.DriverDataType.Float64,
-            MtCategory: "SAMPLE",
-            MtType: "POSITION",
-            MtSubType: "ACTUAL",
-            Units: "MILLIMETER");
+            MtCategory: "SAMPLE");
 
         tag.FullName.ShouldBe("dtop_2");
         tag.DriverDataType.ShouldBe(ZB.MOM.WW.OtOpcUa.Core.Abstractions.DriverDataType.Float64);
         tag.IsArray.ShouldBeFalse();
         tag.ArrayDim.ShouldBe(0);
         tag.MtCategory.ShouldBe("SAMPLE");
-        tag.MtType.ShouldBe("POSITION");
-        tag.MtSubType.ShouldBe("ACTUAL");
-        tag.Units.ShouldBe("MILLIMETER");
+    }
+
+    /// <summary>
+    ///     Review 2026-10-21 T-3: mtType / mtSubType / units were deleted from the definition as dead, but a stored
+    ///     config that still carries them — in tags[] or in a raw tag's TagConfig blob — must keep loading.
+    /// </summary>
+    [Fact]
+    public void Stored_configs_carrying_the_deleted_metadata_keys_still_load()
+    {
+        const string config = """
+            {
+              "agentUri": "http://agent:5000",
+              "tags": [ { "fullName": "dev1_pos", "driverDataType": "Float64", "mtCategory": "SAMPLE",
+                          "mtType": "POSITION", "mtSubType": "ACTUAL", "units": "MILLIMETER" } ]
+            }
+            """;
+
+        var options = MTConnectDriver.ParseOptions("mt-t3", config);
+
+        options.Tags.ShouldHaveSingleItem().ShouldBe(new MTConnectTagDefinition(
+            "dev1_pos", ZB.MOM.WW.OtOpcUa.Core.Abstractions.DriverDataType.Float64, MtCategory: "SAMPLE"));
+
+        MTConnectTagDefinitionFactory.TryFromTagConfig(
+                """{ "dataItemId": "dev1_pos", "dataType": "Float64", "mtCategory": "SAMPLE", "mtType": "POSITION", "mtSubType": "ACTUAL", "units": "MILLIMETER" }""",
+                out var dataItemId, out var authored)
+            .ShouldBeTrue();
+        dataItemId.ShouldBe("dev1_pos");
+        authored.ShouldNotBeNull().MtCategory.ShouldBe("SAMPLE");
     }
 }
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests/MTConnectObservationIndexTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests/MTConnectObservationIndexTests.cs
index 8b2c614a..d8aab2f8 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests/MTConnectObservationIndexTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests/MTConnectObservationIndexTests.cs
@@ -502,14 +502,13 @@ public sealed class MTConnectObservationIndexTests
         idx.Get("dev1_vibration_ts").StatusCode.ShouldBe(BadNotSupported);
     }
 
-    /// <summary>The parser carries the observation's own sampleCount / sampleRate attributes.</summary>
+    /// <summary>The parser carries the observation's own sampleCount (sampleRate is not parsed — T-3: nothing read it).</summary>
     [Fact]
-    public void Parser_carries_time_series_sampleCount_and_sampleRate()
+    public void Parser_carries_time_series_sampleCount()
     {
         var obs = ParseFixture(CurrentFixture).Observations.Single(o => o.DataItemId == "dev1_vibration_ts");
 
         obs.SampleCount.ShouldBe(10);
-        obs.SampleRate.ShouldBe(100.0);
         ParseFixture(CurrentFixture).Observations.Single(o => o.DataItemId == "dev1_pos").SampleCount.ShouldBeNull();
     }