The messages about old tapes playing perfectly after decades match my
experience. All of the tapes I recorded as long as 45 years ago on Scotch 150 and
200, poorly stored for many years in non-air-conditioned environments, play
without problems. Also many tapes I own that another collector made between 1956
and 1960 on a variety of brands (Audiotape, Irish, and Scotch).
The one thing they all have in common is that they are on a Mylar base.
Acetate is often a different story (i.e. mess), as we know.