This is a story of a personal laptop of mine. Upgrading from Win 7 to win 8 with paid upgrade sometime after win 8 was 'stable'
The upgrade tool works fine until it doesn't.
When it chooses not to work, it will have you DL the upgrade files, as well as updates to OS, this can take forever and is a major point of failure for techs. (random hangs, reboots, loops, you name it)
But the really evil bullshit actually happens on successful upgrade. Oh that tool that said your laptop could 'upgrade fine' now can't, so sick of the BS revert to old installation.
Jk to find its no longer a valid bootable os now. had to repair win 7 installation to make bootable and was asked for product key... what? entered mine, sticker still gleaming on my laptop... Microsoft says invalid key! No worries, must be an accident, call MS CS. Am told that upon upgrading even though incomplete, I had willingly surrendered my old product key and it could never be used again. Ok... ask MS CS rep to please issue a new one? He says happily, but they no longer sell keys for windows 7, I could either buy an enterprise edition from them for if I remember correctly $7-800. In shock I looked it up and found at bestbuy for i think was 120...was advised to purchase from bestbuy as MS couldn't offer me the same(
incidentally not long after this was when they extended the EOL timeline for win7).
Screw all that noise, I just ran a SLIC and never thought about it again, laptop's still chugging along today.
So personal anecdotes whatever, but I have worked on far more than my share of PCs, and upgrading became so convoluted early on it was invariably 100x faster and easier to backup and clean install. Even when everything 'just works' when upgrading, sometimes it doesn't. You will have errors everywhere, random hangs reboots etc.
It's infuriating and it has persisted as an issue from Win XP to 10.
The upgrade path is only from Windows 7 to Windows 10 as far as I am aware. Microsoft extended licenses so that license for Windows 7 are valid for Windows 10 and vice versa. This might unfortunately have been after your story.
Windows XP never had an upgrade path (couldn't even change hardware like the motherboard safely) so it's progress in my mind. Windows 8 was a mess that was dropped shortly after release, I am sorry for all the souls who had to try it.
There is a very good backup tool embedded since Windows 7 that allows to snapshot and restore the system. Highly recommend to use.
Microsoft really wants Windows 7 to go away and they actually give the tools to do so. I think it's great!