There's a difference between classic porn studios and Treasure Island Media (TIM) and other 'documentary-style' studios. I believe classic studios try to script out their scenes more completely while Treasure Island spends much more time selecting their participants and then letting scenes evolve as they happen.
I worked with Max Sohl (TIM's NYC-based producer) begining with his first DVD ("Dawson's 20 Load Weekend") and in five subsequent DVDs. Max's casting interview focused on finding out what were my strongest turn-ons and fantasies (bareback topping, gang-bangs, rimming and felching). He took the expected dick, body and face videos/photos. After a number of weeks, he had lined up a considerable stable of like-minded and nicely hung tops. Max had already lined up an eager bottom (Dawson, of course) who selected the tops he wanted to fuck him. Dawson clearly wanted to be the receiver of what all of us tops wanted to do to him. On the night of the scene, tops were told that payment would require a 'money shot'/proof of cumming. But, frankly, nothing else was directed. The tops were just corralled in a separate area until the filming was about to start and Dawson was ready in a dungeon/gym area. The fixed cameras and camera men just captured what transpired over the next 90-120 minutes after we were set loose. All was bareback, of course, and most guys pulled out just as they were cumming and then shoved it back in Dawson's ass. I delivered Dawson's last load of that scene completely, and as deeply, in his ass as I could because, frankly, it was how I most wanted to cum (payment be damned). It turned out that Max had no problems with that. In later films, I believe Max relaxed his requirement to give an external 'money shot' and, in one DVD ("Loaded'), he insisted that tops do their best to give an internal cum.
So, for Treasure Island's bareback scenes, I think tops have much more flexibility in whether they truly breed/inseminate their bottom or whether they showed some cum before they shoved their dicks in their bottom's ass to finish.
Hope this gives you more background - frankly I love most documentary-style porn because it is driven much more by genuine lust and virtually none by directing.