What about when it comes to trying to credit people for the game?  What if I ended up downloading something from Open Game Art and its not properly labled so I end up forgetting who originally uploaded it?  Would it be okay to just credit Open Game Art and their users?

I would still make as many efforts as I'd be able to credit people and let them know if any of their assets have been used in a project of mine, but its just a what if scenario.  Because particularly for sound effects I download and stock up on sound effects from many different & sometimes random websites so its difficult to remember all the users or sites to be credited especially if the audio files aren't labled enough for me to know who should be credited.