I think you're probably missing the CG for Marc's bad ending. If you follow the guide below for the "Presentation Matters" ending I believe that should probably unlock it.
https://steamcommunity.com/sharedfiles/filedetails/?id=1647304903
It has been a while but I believe Danny's 3rd CG happens towards the end of Chapter 4 and requires a specific "affection" score. If you managed to get the best ending without unlocking this CG you probably barely missed the required stat.
I would recommend (if you haven't already) trying to follow a guide that helps you get your score as high as possible through this area so you will be sure to unlock it.