I would guess that your IT department created new accounts for these users on their return instead of restoring their previous accounts. That means that from Laserfiche's perspective, these are separate users that happen to have identical names but are otherwise unrelated. When you search by name, the system first turns that into a security identifier, which is how users are identified internally. If the system knows the identifier for a name, it won't look it up again or look for other users who happen to have the same name. I think this is why you are reliably finding documents associated with their old identities.

There is a table in the database where this information is stored, and if it's removed the system should look up the new identifier. Modifying this data isn't really something you should do yourself though. I'd suggest you work with your Solution Provider to open a support case and they can walk you through the steps.