Perhaps you didn't click the correct submenu? Took me a bit to figure it out. Any scene you've already viewed is viewable but when you click on scene replays, there's also a little submenu of little chibi heads of the guys for a specific guy's scenes. I didn't see that at first myself so maybe that's what you're talking about? If not, sorry I couldn't be of help.
Well, some MC scenes are general group events... I heard there's an NSFW one where you hafta own a vibrator, and an all-in-one computer and masturbate a lot to get a scene? I have yet to see a full cg guide, but if you screenshot which ones you're missing, maybe one of the fans can help you. I find everyone is being pretty helpful in the comments section. :)