AL and it's various earlier incarnations are a sizable amount by themselves. Just AL is probably in the 30s or 40s and I have only done a couple of the hardbacks. People joining and leaving, plus if a DM didn't make it the other tables incorporating in those players for the night (and vice versa, going to play at another table because the DM was out that week). I'd say 15 were fairly regular.
For long term groups it's different. Okay, I guess you could say that I have a couple of distinct gaming groups over the years, each running mutliple campaigns with various subsets of players, plus some external players who were just for that campaign. Let me estimate a group of 20, a group of 12-15, and a group of 10. Oh, and a group of 7. Oh wait, college, add another 15-20 ... eh, make that 10-15, some of those college buddies are included in other groups since.
One shots and short-form are probably 15-20 unique - even with the decades I've been gaming I don't do a lot of them, and often I'm invited to them by people I already have played with so there's only a few new per game.
I haven't attended a lot of different conventions, but one in particular I went to for a good number of years and ran at them for more years. When you run 5-6 sessions of 6-12 players with little overlap, that's a huge number of players right there. And that's just one year. Though there's a good amount of overlap in players from year to year. Still, it easily brings it over 200 (hey, there's no 201-300 bucket!), and could bring it to the 300+ bucket, so I voted there.
