Heroes 3 (HEROECOPALKA)

Are there any other reasons why a free hero might not appear in the tavern?

Or is that even possible? 0o..
As far as I remember, a hero cannot be recruited if:
1) He is sitting at a computer in the tavern.
2) He is disabled in the map settings.
Hmm, I don't remember if external prisons count or not...??^^