No idea regarding format, but tape is famously quite hardy if stored well from what I've been led to understand. Not to mention datahoarders are way more common than one thinks, so I wouldn't be surprised if there are some decent number of old treasure troves out there just waiting to be recovered.
We've got a few stacks of PDP-11 tape packs at work, and someday I'd like to see what's on them. I've figured my best bet is probably to learn how to fix the original hardware enough to get it functioning, then connect the tape drive to a modern computer somehow to image the tapes. I haven't pursued it further because I'm sure it's all cash register records from the 80s if they're even still intact.
