It is one of the things which people complain about the most. You can get some idea by checking the gallery (which can be seen through the load/save menu), images you haven't seen will be blacked out and videos will have an X through them, but it isn't super helpful as there isn't any context to help you understand either what they contain or how to get them.Is there a way to know how many scenes are yet to be unlocked in the game? The % of completion we have with the different characters?
The ingame character screen or even the gallery seem useless in that regard. I have no idea if I unlocked all scenes with a character or if I need to keep griding.