He definitely is the first human Hunter but there's no official info about how many of them existed in the past. Probably you could count those that appear in the Forge, though, I think it has all of them.
I hear you, I've been thinking about it too and I just think there'll be some insight into this in S3, since this was a huge deal. And I'm really fascinated by this; I think it may have something to do with Jim thinking he'd be better off being a troll sometimes.