diff --git a/docs/proposals/device-identity.md b/docs/proposals/device-identity.md
index c94b718..e97de87 100644
--- a/docs/proposals/device-identity.md
+++ b/docs/proposals/device-identity.md
@@ -120,6 +120,21 @@ and no new read path: the collector already opens
 `HKLM:\SOFTWARE\GE\ShopDB` (and the `WOW6432Node` variant) for `BaseUrl` and
 `ApiToken`, and `Install-GEEnforce.ps1` already writes that key.
 
+**One value, every family.** `DeviceId` is a single registry value, not a key
+per device type. The client sends one field and the pc-type decides which sync
+consumes it, exactly as `asset-id.txt` works in phase 1, so:
+
+| Bay | `DeviceId` holds | Replaces |
+|---|---|---|
+| CMM | the instrument's `assetnumber` | `cmmid.txt` as IDENTITY only |
+| Keyence | the instrument's `assetnumber` | nothing; had none |
+| Genspect | the instrument's `assetnumber` | nothing; had none |
+| wax-trace | the instrument's `assetnumber` | nothing; had none |
+| part marker | the marker's `assetnumber` | minting from the hostname |
+
+A device family added later through `subordinatedevice_<pctype>` is covered on
+the day it is declared, with no client change and no new registry value.
+
 Resolution order after phase 3:
 
 1. `HKLM:\SOFTWARE\GE\ShopDB\DeviceId`