Should I Keep USPS Souvenir Pages In Original Mail Packages?

One would think the expensive plastic black-page, clear-pocket stock pages were "archival safe" for stamps, mint or used (off-paper). My big initial investment in them, with varying size pockets, from one popular maker in early 1990s, saw all the clear plastic turn yellow. (Imagine viewing your "collection" portion of your accumulations through these, especially the color varieties!)

I was very upset, you can imagine. I believe circa 2010 I had the manufacturer make me whole by sending new ones. There was some mumbling on their part that "some were made in West Germany" (or East Germany, I can't recall) and were discontinued for a better source.

Care to share which brand it was?

John