Ahhh... you all focus on the girls. If she pukes it must be real. Firstly yes there are girl who don't like sucking cocks and maybe more than half of the girls don't like to swallow, but to make such a vid, it takes only one exceptional girl. And once she overcome whatever barrier to swallow one load, she can swallow a hundred. It's like buffalo wings, the first couple might burn, but after that eating 10 or 50 is only getting easier. The only limit is the size of your stomach.
I tend to doubt these not for the girls, but for the guys. Getting 120 men, do you give them private rooms? (doubt it) girl mags (yes) fluffers (no, I'd guess). 100 guys, in a less-than-ideal environment, with no hot girl in sight. With 10 guys it's not hard at least for each of them to visually see the girl who promise to drink your sperm, but 100 guys, it has to be in your head only, plus the girl mag. Speaking for myself, I doubt I will produce a full load in such as situation. Call me a doubting thomas, when it comes to collecting a pint, a jug of semen in a reasonably cost/effort efficient way.
Also how does the gagging, crying and puking fit into this subculture? I'm not sure. If such things are part of the turn-on, it's easy enough (after a little training/practice) to gag, cry and puke on cue. I just doubt that a girl would agree to make such a vid if it makes her hurt or uncomfortable.
I do not doubt a lot of real sperm is put in the mug. I just doubt that no additive was added to fill up the total volume. And since I am a nice guy, I'd add a little flavor or smell to help it goes down easy.