If the aircraft has had a significant safety event, all parties involved should be quite cognisant that data needs to be preserved. When that doesn’t happen, it smells mighty fishy right away.
Two examples that come to mind involved the crew erasing the CVR in one instance and a corrupt manager ensuring overwrite in another.
It happens. And it happens in organisations with all the right bits of paper and post holders. None of it is worth a fart if the players have poor ethics and there is weak oversight.