It would not be that difficult for JAV directors to fake a defloration sex scene.
There must be a laboratory in Japan which produces a non-toxic red liquid which could be passed off as blood. In the U.S.A., Herschell Gordon Lewis' original gore movies ("Blood Feast") used Barfred Blood {name of the lab}.
The off-camera secret to this then becomes using a small plastic bag (usually used to hold a lapel pin) with a zipping closure. Put the fake blood in the bag. Close the bag. Insert the bag in our female's pussy. With any amount of hard thrusting by the male, the bag will rupture open, and the liquid will ooze out of the female's pussy.
Granted, this mandates the main camera angle must be directly pointed at the female's pussy - nothing from the front or side [i.e.: Missionary Position]. Because the viewer must be shown when the blood begins flowing out.