Reference to deleted Exchange 2003 database in Exchange 2016 to 2019 migration

We recently migrated from Exchange 2010 (as part of SBS2011) to Exchange 2016 on-premises as a stepping stone to Exchange 2019.  The migration went as planned to Exchange 2016, and Exchange 2010 was removed cleanly.  We now have Exchange 2019 installed, and are ready to migrate mailboxes.  However, we get the following message when opening Recipients, Migration, clicking "+" to start a new migration batch, choosing "Move to a different database", then clicking "+" to select users:

Couldn't find database "domain.local/Configuration/Deleted Objects/Mailbox Store (SBSERVER) DEL:e2afb0df-946d-4e30-99fc-9897ccd47835". Make sure you have typed it correctly.

Now SBSERVER is the old SBS2003 / Exchange 2003 server that was removed (cleanly, we thought) several years ago.  It would appear that we can still search for mailboxes to move, and use the Exchange shell to move mailboxes, but nevertheless we would prefer to clean up this reference to the old server.  Presumably this would be in ADSIedit, but there is nothing under the Configuration context in:

CN=Configuration, DC=Domain_Name,DC=local
          CN=Services
               CN=Microsoft Exchange
                    CN=Your_Organization_Name
                         CN=Administrative Groups
                              CN=first administrative group
                                   CN=Servers

In fact, the entry "CN=Servers" is already missing entirely.

How can we prevent this error from occurring?