This has happened to a product I worked on. There were 2 companies working on it, and when we were done there were 2 backups that I made after we'd finished it.
Backup #1 (USB HD, kept by development company A) was lost in a flood. Of course, this sort of thing is why you have 2+ backups...
Backup #2 (USB HD, kept by development company B, the one I worked for) was lent to the client after they wanted to take a copy of it themselves. Then fast forward 6 months, and:
US: Please would you return our backup drive of product XYZ?
THEM: [paraphrased] Who are you?
This product was a one-off, and not key to company B, so nobody chased this up (not that they could do much anyway because the backup drive was presumed lost forever). We only found out about the loss of backup #1 when company A asked us for our backup, because they needed the code for a project they were thinking of doing...
Backup #1 (USB HD, kept by development company A) was lost in a flood. Of course, this sort of thing is why you have 2+ backups...
Backup #2 (USB HD, kept by development company B, the one I worked for) was lent to the client after they wanted to take a copy of it themselves. Then fast forward 6 months, and:
This product was a one-off, and not key to company B, so nobody chased this up (not that they could do much anyway because the backup drive was presumed lost forever). We only found out about the loss of backup #1 when company A asked us for our backup, because they needed the code for a project they were thinking of doing...