"It isn't obvious from your posts whether your 5.0.2 ATV is currently broken."
No its working fine, I want to upgrade for more AppleTV features released since then.
"most jailbrakes disable the upgrade facility."
It used to upgrade a while back, and I remember having to jailbreak again. I was fine with that and I understand it. But it just stopped one day without me knowing, so I did not know there were upgrades. I expected it to upgrade like it used to.
"and periodically used the Maintenance / Settings / Manage Backups / Backup My Firmware"
Never did this "periodically" because I was always on version 5.0.2. I never had a need to do this periodically, never knew there were more recent updates, no nitifcation came in AppleTV like it used to.
"you might have saved blobs for other versions that you haven't actually installed"
I have not checked, but I cant see why I would as I never ran the backup periodically and therefore catch the 5.2 version when (if) it was there but not installed.
I reckon I am buggered.