Comment by tgtweak

There is one parity bit per 8 data bits, which is decently resilient - plus the recovery is pretty simple on the occasional bit flip. Combine that with the fact you can reference other sources to make up for missing/corrupted files - I think the chance that this is recoverable is pretty high provided the machine reading it is high quality. Checksumming on the source was unfortunately not commonplace until Unix 7, so it's unlikely there was any software-level integrity checks here. The tape looks like it was stored in a sealed container which is a very good sign. Those older tapes are actually more resilient than the later generation of tapes, and don't usually degrade the same way even with exposure to humidity.