[Stephen]

Of all the 70s and 80s records I've got and listened to sound fine.

Got a bunch of his old 7 inch singles also mostly from the 60s.

That tape you got it was probably reproduced in the exact same way with the same equipment. However as tapes are reproduced the master tapes will wear out over time giving poorer sound quality much like when video tapes are copied that often they would eventually be of a lesser quality.

That introduces that benefits of digital mastering, every version produced from it will always sound the same it doesn't deteriorate.