Decal preservation

Just wondering if there is any wisdom on decal preservation techniques. I have several kits i have had sitting on the shelves, i guess to long. I have begun building some of them and all the decals have yellowed abit or fall apart when applying. I tried the sun to reduce the yellowing, but on a white car it doesn't fix it totally. So either i need to scan them as soon as i purchase the kit and plan on reproducing them when ready to build, or find someway to keep them pristine during the time sitting on my shelves. What does everyone do to minimize this problem?

Thanks

I'd like to hear others thoughts on this too,
I have very many vintage kits that I'd like to preserve as much as poss.

I was going to just get acid free archival tissue to cover the sheet and then
place in a acid free archival plastic comic bag, and then maybe slide them in a book.

Keeping them with the instruction sheet is bad news, those were never made for long life.

Cool another person from New England! As for your question, I have no idea...lol I want to know though

I keep all my decal sheets in a folder. The type with clear plastic sleeves. I keep the folder in a dark cupboard well away from the sun and it also keeps the decals cool. So far I have never had any problems when I come to use them and the decals are as good as new. I've stored some sheets for 3-4 years and they are still in pristine condition. When I build the models now I overcoat the decals with 2K clear and this seems, so far at least, to stop them from yellowing over time. Many of the models I've built that I didn't clear have yellowed, but the 2K cleared ones are still good after 18 months to 2 years. Only time will tell I suppose...???