If this weren’t a concern, regulations would demand immediate deletion of data.
there's a whole lot of people in here who are way too quick to assume that just because one part of a permanent deletion process was inadvertently triggered and then caught while they still had backups, their whole permanent deletion process is a lie.
You seem to be right-ish, while the gdpr in certain circumstances allows you to keep backups of data that should have been deleted it seems like they are trying to discourage it in the future.
> ...It is, however, important to note that where data put beyond use is still held it might need to be provided in response to a court order. Therefore data controllers should work towards technical solutions to prevent deletion problems recurring in the future.
That can mean as much as "you have to encrypt everything with a separate key, so that you can destroy the key for the given (say, personally identifiable) dataset making its retrieval irrecoverable"
I'm not saying that's the particular compliance reason they had here, or that the analysis you're giving is wrong, either. There is an interpretation where either of these ideas could be the correct one.