diff --git a/tests/ZB.MOM.WW.ScadaBridge.Commons.Tests/Types/AttributeValueCodecTests.cs b/tests/ZB.MOM.WW.ScadaBridge.Commons.Tests/Types/AttributeValueCodecTests.cs
index 15229611..fa717bdb 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.Commons.Tests/Types/AttributeValueCodecTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.Commons.Tests/Types/AttributeValueCodecTests.cs
@@ -93,10 +93,28 @@ public class AttributeValueCodecTests
     {
         var json = AttributeValueCodec.Encode(
             new List<DateTime> { new(2026, 6, 16, 0, 0, 0, DateTimeKind.Utc) });
+        Assert.StartsWith("[\"", json);   // DateTime list must be an array of quoted strings
         Assert.Contains("2026-06-16T00:00:00", json);
         Assert.DoesNotContain("06/16/2026", json);
     }
 
+    [Fact]
+    public void Decode_OldStringFloatForm_BackwardCompatible()
+    {
+        var back = (IList<float>)AttributeValueCodec.Decode("[\"1.5\",\"2.25\"]", DataType.List, DataType.Float)!;
+        Assert.Equal(new[] { 1.5f, 2.25f }, back);
+    }
+
+    [Fact]
+    public void Decode_OldStringDateTimeForm_BackwardCompatible()
+    {
+        // The pre-native codec encoded DateTime via IFormattable.ToString(null, InvariantCulture):
+        // "06/16/2026 12:30:45" (US-invariant, no 'T'/'Z'). New Decode must still parse it.
+        var back = (IList<DateTime>)AttributeValueCodec.Decode(
+            "[\"06/16/2026 12:30:45\"]", DataType.List, DataType.DateTime)!;
+        Assert.Equal(new DateTime(2026, 6, 16, 12, 30, 45, DateTimeKind.Unspecified), back[0]);
+    }
+
     [Fact]
     public void Decode_NewNativeIntForm_Parses()
     {