Too many MC's?

i have a timeline that has 17 different years on it. when you click a year it takes you to a movie clip (so there are 17 mc’s). the problem i’m having is that when i test the movie, on a few of the mc’s there’s stuff showing through (from where, i don’t know). i have all the mc’s in a folder on the main timeline, which is also where the “timeline” and it’s year buttons are.
this is probably confusing without actually seeing it…i haven’t checked but i’m sure the .fla file is huge. i just thought i’d ask though in case anyone knows a better way to organize the mc’s so nothing shows through