I wonder what their data deletion policies really are for something like Photos. I deleted all my old photos weeks ago but when I pull down the archive of my Google data, they're still there. With such a policy, I could see that data sitting around for years while Google claims that it's in the process of deletion, something that is not actual deletion. Then again, I doubt they actually ever delete anything.
In which case, you likley didn't delete them correctly.
If you delete them from your device, it doesn't delete the cloud copy.
If you delete from an album, it removes the image from the album, but not from your account.
Google's privacy policy says has limits to delete user data, and I can assure you they are very strict about that. (Lots of data is deleted within hours, but the multiple days is to ensure all backups of it are gone too)
There are whole teams and pipelines dedicated to making sure data is deleted on all media, tapes included. The long tail can be affected by things such as a machine holding a bunch of GFS chunks from your files that went to the hardware repair queue in the meantime. Those chunks might not even be that useful without the others stored on other machines, but in the general case you can't make guarantees that e.g. they don't hold information that a skilled person could use to identify you.
Also, I'm not sure if photos has this, but you also need to "empty the trash" in your drive account after you delete something before it will be actually deleted.
IIRC it gets auto-deleted after 30 days or something.
