Very good breakdown of the ways to activate Windows 10. Most people don't even realize you can still use a windows 7 key to activate, only after you get into windows, and not during the setup process. I believe this will probably stop working Jan 1, 2020, when Microsoft stops support for windows 7.
One thing that I was hoping for some explanation on key activations, I have seen how some Youtuber's have tied their windows 10 keys to their Microsoft account. Then they only need a handfull of keys, like one for each motherboard vendor, and during setup, then sign into their Microsoft account, and select the key that corresponds to the motherboard their are reviewing. So they can move the keys around, and as long as it was the same brand of motherboard it would activate for that computer, and no longer be active on the old system. Any thoughts on how this works? Any limitations on how many moves, is this method valid for years so you would never have to buy another key if you stayed with one particular favorite motherboard vendor?