Google assured me that it had removed everything
Discussion
There are absolutely no reasons no to trust them, right? Right?
It's not a question of trust. Google has such a procedure, a private relay owner may or may not have it (nostr.wine seems to keep this data for six months).
While I agree that Google has to follow formal procedures and do what they say they do, there is always a chance that they don't do that because of a human mistake, negligence or even technical inability. For example there was a time when FB did their backup using simple consumer Bluray disks. They are write once only. It seems unlikely to me they would go find a specific set of disks where you files went, had you requested you profile removal. And now Microsoft just announced they are going to write their backups into sapphire glass where it could be stored for thousands of years with an incredible density. No way they would ever really completely remove any data.