Thank you very much, nobiot - you led me to the solution.
I had already run org-roam-update-org-id-locations, but the migrated backlinks weren’t showing up. Before I searched up how to how to delete the db and rebuild it from scratch, I looked through all the org-roam-... commands for anything related to a database.
Doing that turned up org-roam-db-sync (synchronize the cache state with the current Org files on-disk). After running the command, the migrated backlinks showed up.
I appreciate the help, as well as the speedy response.
~ML