When I build a new PC, I could not transfer my old 7 pro retail license, even though it worked fine on my old PC running Windows 10 and it even said it was a digital license connected to my MS account.

So I bought a Win 10 pro key from one of the ebay resellers aber everything was fine... until it wasn't. I updated the firmware for my mainboard and Windows took that for a replacement of hardware. Troubleshooter did not show three option "I recently changed my hardware" and did not give me the option to call Microsoft's support.

Turns out it was a "one time install" key which was invalidated by changing the hardware. So it couldn't activate a second time. And since the key seller was out of business at that time (they'll change accounts every few months), I had no way of getting the key replaced.

Luckily, I still had an old Windows 7 COA with key and CD lying around from an old Dell business Workstation. That activated just fine.

But yeah, even if you have a valid license connected to your Microsoft account, there's no way of seeing it in your account, and it's not guaranteed MS will honor it.