I think the way it works is, so long as you didn't find them a home, they can wait basically forever to hop into someone's town. I could definitely be wrong, though. If you feel bad you could warn people so that maybe only people with 10 will visit. Or, you could say that can always happen with online trading, and that people with 9 villagers should always accept that risk.
I'm not blaming you, btw, I shoulda been more careful.