Thanks for the heads-up, I was wondering, do you have some order of magnitude of
how many accounts we're talking about?

That's a little less than 2000 accounts (1840).
 
Could it be possible to check how many of these people have a FAS account with
the same email?

Hmm, I'm not sure how to do that without hammering the API. Ideas?

(I know I logged in on HK w/ persona a while back and I was
using the same email as is attached to my FAS account, for example).

For the accounts that used Persona with an @fedoraproject address, I migrated them as if they had logged in through FAS. That's not the majority of FAS & Persona users though because the FAS auth returns the main email address to the app, not the @fedoraproject alias. But that's still a few.

Aurélien