Here’s one way it happens:
Run across mix notes in a sketchbook excavated from an attic box.
Go downstairs & rifle for old CD binders to see if a backup disc exists.
See if one of the drives works.
In the early aughts, I was at my Bakersfield storage space with another musician, transferring a few pieces of gear in & out. The San Joaquin Valley was summering a typical heatwave making the space an oven. Most of my other possessions were there, like a taxidermed caiman head. When we moved the caiman, it felt sticky — maybe even sweaty.
We laughed it off over lunch & traveled north to a San Francisco gig where, right before stage time, the musician with me suddenly vomited near the beer cooler. The spew was tar black, without a sheen.
The show went off with the usual hitches.
The pic is of two drives I’ve used with my Roland 2480 recorder. The one on the left is the original from about 2000 that died when the pandemic began. The two-tone on the right is from a thrilling eBay auction a few years ago. It still works.
Their common affliction, though, is the same stickiness that I remember from that caiman. It’s just on their sides where it looks like parenthesis. The sections are also slightly rubbery. I don't know what its casing material is, but I’ve used the new one twice now & still haven’t experienced any ectoplasm.
Recover the data into the Roland.
Try to hold back, but commence with second-guessed tweaks.
Impulsively commit.
Search for your one pair of RCA-to-1/4” connection cables for an hour, then find them where you conveniently left them for easy access in the last place you look.
Copy the mix onto the laptop via another decades-old deathbed drive that clicks & groans, then exhales when it’s done as if exhausted from depression. Blindly traipse through a few more homestretch device-chain generational differences until a workaround technically allows you to not listen back out of fear of what you won't find.

ACH! Technology! (As my mom used to say.) The cables I’ve accumulated! I know that sticky stuff well from old equipment stored for years. The hand sanitizer works!
Try cleaning the rubbery parts with liberal amounts of hand sanitizer, and then wiping clean with a paper towel. It sounds weird, but it works.