The same problem exists with photos. Photos taken during the Civil War are more permanent than those taken since the fifties. Inks fade and disappear whereas those old silver emulsions never fade.
I recently transferred about 800 kodachrome and ektachrome slides taken in Viet Nam to digital format. About 2/3’s of them were OK, but the remaining 1/3 were color faded in all but the reds. By faded, I mean there was no trace of any color except red.
Ektachrome slides are all red. I had that issue as well. Kodachrome slides from the ‘50’s held up pretty well.
Maybe they were taken in Pleasantville?