Funny, this was may take on the article too. I suppose one could download x amount of files from one cloud storage and upload it to another to see if there is any obvious discrepancy. Perhaps Apple are still using their old file system format for icloud? It's been around for a good few years now and perhaps they simply haven't bothered to ever change the type of storage format they use. Maybe those with older accounts have their images / videos on the 'older' drives?
I don't believe iCloud is a filesystem, it's not block-level. It's object-level, like S3, with a bunch of OS-side jank to make it look like a conventional directory and filesystem (which often fails miserably and dangerously).
It's similar levels of reliability to an FTP account mounted with curlftpfs[1] - except the latter at least fails in understandable ways and can be debugged.
That's exactly my mental model of it as well, some janky home made s3 fixed with tape. I really advise anybody to save their data somewhere else as well before in inevitably stops working.
