YES ...
the information you crave is @ the Windows10 update page. Not every pc / laptop / tablet is setup the same, perhaps some proprietary peripherals are causing the issue. Apps / processes running in the background (or foreground) won't be upgradeable, ...
There could be a hundred reasons WHY your upgrades are failing - I'd imagine you have some special circumstances.
... and 9 PCs does seem a tad excessive
Totally aware not every PC is the same yet it still begs the questions… “Why were previous OSs so forgiving compared to W10?”. The last time I can remember having major upgrade/install issues was with Vista (on one PC only), and rarely have I waited more than a couple of days before upgrading to the latest OS either.
The majority of my hardware is from varying manufactures (Acer/Asus/HP/Lenovo/Samsung/Toshiba) so we are not talking one brand here, i5 or better, 6 gigs ram or better, AMD or Nvidia dedicated graphics with the odd Intel onboard, SSDs, nothing I’d consider having special circumstances, you'd think there'd be no issues with the majority in that one try is all it takes.
It’s more than 9 but do agree with the excessive part LOL. The thing is, they do not all get used that much and none are left on continuously (lights out when not in use), and every one is kept fully up-to-date in every aspect, as a matter of fact, on most the OS would be considered freshly updated or installed to a degree since W10 first became RTM. I am very meticulous about keeping my devices in tip top running order and one would be hard-pressed to hard to find any better maintained systems… Maybe my nemesis?
Having so many devices, for me anyways, just solidifies my thinking that MS kind of missed the boat somewhat with W10, maybe they chose to forgo supporting anything (out of the box) 1.5 years and older... My 8+ year old Toshiba (A200-TJ9) though was the only lappy in round one to be error and trouble free, strange but true, haven’t bothered to introduced it to the Fall Update yet.
Have to throw this in as it seem pretty prevalent when scouting forums for solutions... Many attribute installation problems with 3rd party software, manly firewalls/antivirus (have not encounter an occurrence where that was the case but understand it), for many years now I've only relied on MSs offerings and have no complaints so far.