diff --git a/docs/drivers/MTConnect.md b/docs/drivers/MTConnect.md
index 210bc10f..d19186f7 100644
--- a/docs/drivers/MTConnect.md
+++ b/docs/drivers/MTConnect.md
@@ -429,6 +429,12 @@ for anything beyond values-and-conditions.
    Warning for differing `RawTagEntry.DeviceName` values stays as defence in
    depth for configs that predate the rule.
 
+   ⚠️ **Upgrade note:** an MTConnect driver that *already* has two or more Device
+   rows fails its next deploy with `MTConnectMultipleDevices` (the rule counts every
+   Device row, enabled or not, because nothing at runtime reads `Device.Enabled`).
+   Before upgrading, move each extra Device's tags under its own MTConnect driver
+   and delete the extra Device rows.
+
    **The write path is the one place a device name is resolved per DataItem**,
    and it does not use `RawTagEntry.DeviceName` either: it reads the owning
    device out of the cached probe model and falls back to the top-level