Reusing W10 Home product key after upgrading to W10 Pro

A long time ago I upgraded a computer from W10 Home to W10 Pro. This was a custom build and both the original W10 Home activation and the new W10 Pro activation were done via product keys ordered from Amazon.

No Microsoft account has ever been involved with either key. Back in May of this year I completely reinstalled Windows but I don't really recall if I had to reactivate the license or not.

And now I'm wondering if I could reuse the original W10 Home product key on another computer, and if it would affect the current W10 Pro activation in any way. Would the original Home product key still be tied to my main computer's motherboard or did that history get wiped when I upgraded to Pro?

This was a custom build and both the original W10 Home activation and the new W10 Pro activation were done via product keys ordered from Amazon.

If you built the computer (vs buying with Win10 preinstalled) and bought separate copies of Home and Pro, then you can use the Home key on another computer. Each version is independent of the other and each key entitles you to put one copy of Win10 on one computer.

I did buy Home and Pro keys completely separately (as in I bought a brand new Pro key for $200 instead of the $100 upgrade) but when I upgraded to Pro way back then I didn't reinstall at the time, I just used the "Change Product Key" button in Settings > Update & Security > Activation, restarted and bam, done.

So basically did the Pro activation key completely kick out the original Home activation key, or something?

When I check my current W10 Pro computer's license via slmgr.vbs /dlv I get the generic key VK7JG-NPHTM-C97JM-9MPGT-3V66T which is apparently the default key for Pro and not the product key I used to activate Pro. I'm supposing that's because I reinstalled but my motherboard already had a Pro license?