Yah, anything left on the clothing (stains, a bit of bmilk, etc) even though it "looks clean" will come out as it sits. Forumula is the worst offender, the oil in there is YUCK and makes huge yellow stains on things in a very short time, even in good conditions.
IF you can control the climate of storage, say, in a spare room instead of the attic/basement/garage, you will reduce the heat/cold exposure and they will be less likely to yellow. Our basement stays about 70 all summer, and 60 all winter, so it's prime storage space. Our attic is about 30 in winter, and over 100 in summer, BAD place to keep things.
I use the cheap boxes at Target that are clear w/solid lids. I write on the outside what's in there (0-3, 3-6, 6-12m, etc). I had rubbermaid tubs too, but they felt funny to me, stickyish. Although if there is risk of water damage, the rubbermaid ones are designed to keep wet out better than the cheaper ones.
Lisa, mama to Lauren, Elliot, angel Marion, and baby due in the fall.