Deregistering an OmniFocus sync client without the desktop version

Just wondering if there is a way to de-register a client without the desktop version (which I do actually have).

Occasionally in the past when upgrading devices or restoring an existing device I’ve ended up with “duplicate” clients synced to the database. The only symptom of this is an ever increasing number of zip files and increasing sync times.

Does an “old” client eventually get purged or does it have to be removed with OSX OF or by Omni?

I ask because I know someone who is thinking of returning to OF after some time, they won’t be getting the desktop version and they’ll probably run into this (if it’s still an issue).