I had a lot to say about that on a thread some 2 - 3 years ago. Neither Asus nor MS seemed willing to reveal just what was going on, and during a conversation with Belarc, they said they can't see them at the moment, 'But we will.' And they can.
In the end, MS offered me a full 8.1 Pro on discs for $45 which I readily accepted.
I've just picked up a Lenovo PC unopened box with 8.1 on a 2 TB drive. It has one of those half hologram stickers.
I've 'upgraded' it to 10, and will look to see what Key is allotted to that install as it's usually different, but I forgot to note the original Key. Despite the computer operating okay on 10, it was still a bad mistake as recently only the original Key on the (disposed of long ago) computer would allow the ISO download for a fresh install. I happened to have the Key but have a feeling I'd have been out of luck without it as MS really do seem to be toughening up on bogus use of their OS's, especially where they're downloaded by request from an automated system.
That computer had, had three Activated OS's in its lifetime, and their system refused all but the original W7.