IIRC inactive accounts were removed with the switchover to Vbullitin but you'd have to confirm that with Karlos.
I wasn't actually involved in the user account import process as vB had all the tools for that built right in.
It was all the non-standard 3rd party xoops modules I worked in migrating.
I know that a few times over the years here there has been some account pruning, but only of users that hadn't logged in for many months.