Recently there have been some threads on disintegrating decals from older kits, and I've experienced this recently on my JunkersJU-52 (decals were toast).
Anytime I get a new kit, or an older kit off ebay, first thing...I always take the decals out and place them in heavy duty acid free clear sheet protectors, and inside the sheet protector I place a sheet of glassine over the front of the decal, which is something stamp collectors use (I'm one of those also). I then place this in a stiff file folder from Staples or the like and it lie flat back in the model box.
This keeps any air or moisture from getting to the decal sheet and it should never yellow if they are new.