We are talking about permanently deleted records. Records TYPO3 deletes in the probably most unexpected circumstance: When someone restores related records with the Recycler module.
Yes, you've been reading right, the restore operation actually removes records. And if those have no soft-delete options set (the famous "deleted" field in the database), the records are gone. Your last resort is the hopefully current back-up.
If this behaviour is known, why wasn't it fixed? Well, we actually tried to, but it turns out that this wasn't exactly the kind of trivial fix done in one hour. It eventually turned out to be unfixable in the released versions. 
TYPO3 version 11 LTS to the rescue
We finally know the malicious behaviour is gone and we can be sure that editors won't destroy their data unnoticed. What a relief.
So isn't this a real good reason to upgrade rather sooner than later? We think it is!