I have a bunch of 4-track and 8-track tape cartridges from the 1960s. I thought the magnetic tape would go bad over the years. Nope. Problem is that the foam and rubber disintegrated on many cartridges, but the magnetic tape is still good. I have a few players and recorders that still work, but shy away from playing the remaining tapes. (Also have some 9-track tape reels from my work on mainframes in the 1970s but no device for them...).
I transferred to digital some 8mm color movies that my father shot between 1938-40. The splices had often dried out and failed, but the films themselves and the color was as if they were shot yesterday. Kodacolor lasts at least!