Even within the same company. Every division has backup processes, only few actually try to recover the data once in a while...
I've ran drills with companies which concluded that the incremental backups couldn't be restored due to some data corruption issue (no readback test was ever done).
Luckily the company also did a full backup every 6 months, so a disaster would have only thrown them back 6 months at max! /s ;)
But yes, some issues were even more simple: I had a case where performing a restore required twice the storage size of the uncompressed data, and the company actually didn't have the infrastructure ready to do that in case of a disaster...
Don't get me wrong, drills are important! You should do them. However backups without a restore drill better than no backups at all. Even if you only get the last full backup, the data from the last 6 months will be the easiest to recreate from scratch if you must.