I just did an import from phpBB3, and none of the imported users can earn trophies. If someone registered after the import, they can earn them though. I tried running the CRON in the Admin panel, and still no luck.
It seems the issue has been solved. After about an hour or so, the trophies that were due for members (and myself) popped up. I'm still unsure why running the CRON for them didn't update them right away though.