https://ico.org.uk/for-organisations/guide-to-data-protectio...
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.
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.