Ok, if it's the same PC and the files show as downloaded but not installed, then you installed them before Dec 17, which was when the download manager was updated to save the install status for each file between sessions.
OK, I'm pretty sure the DownLoad manager did upgrade today,
It looks as though I bought the upgrade on 17th, so probably
just missed the update of the download manager.
I can confirm that the version I now have, 1.0.87, reports the various software and packs installed as I'd expected, though it dodn't before I installed them all again. That appears to conflict with Simon's answer as most of the files were already installed, hence my puzzlement.
I'll mark the thread resolved.
Thanks guys.