Ok, not so much a discussion item as a how'd it go report...
Updated one of my lessor laptops... succeeded on the second try.
I decided to use the Media Creation Tool to jump start the process since I hadn't reserved ahead of time or installed the get Windows 10 app.
I figured since I have several to update I could save time and bandwidth by creating a USB drive for installing.
It created and verified the USB and I verified it would boot if needed.
Then from within Windows 8.1 I ran setup... it went through some preliminaries and got to asking for the Key which AFAIK it should have skipped and I was stuck... I didn't have a key and could not proceed.
Went back and reran the Tool and used the "Update this machine now" option which downloaded W10 all over again and this went through the Upgrade without any problems, never saw a screen for entering a key (Which I shouldn't have).
One down.
Not sure why the USB method failed...
Note: If you boot off the USB and you select the Update Option it will tell you to Update you MUST run setup from within Windows. I wonder why they have that option listed then, seems silly. Maybe that GWX app performs the missing magic...