IIRC, Kodachrome slides used to (maybe still) in processing have a lacquer overcoating as a final step, which would seal the film against environmental vapors contacting the emulsion. No Ektachrome has this. I think, from my own Ektachrome processing from the mid-1960's to the present, that with Ektachrome Process E-4, the films started exhibiting more stable dyes. I have many images made on Ektachrome E-4 films that are just fine, but I never put them in slide pages that had problems.