I think the "backup copy" angle is spin. From everything I've read, it sounds like the relevant documents are multiple DRAFTS of the eventual memo.
I don't think he took multiple copies of the same memo. I think he took multiple (different) drafts which led to the official memo.
I agree. The damning documents that needed to be removed show the deliberate steps taken to change/fabricate "facts" and arrive at the final fiction.
There may well be a backup for that final document--but not for the preliminary notes and drafts that went into creating it. Without backups for those, all we have is copies of the polished lie, not the succession of smoking guns that blueprint the lie. And that's what Berger was after.