I was lucky to receive 10 Windows 7 and Visual Studio Ultimate keys for personal use, in the Windows 7 era.

Once the "you can use Windows 7 keys to activate Windows 8/10" thing, combined with Microsoft accounts came around, I created 10 Microsoft accounts with 10 of my email addresses.

I've been able to activate Windows versions 7-11 with all 10 keys (and I can change to older Windows without issue) and been able to upgrade Visual Studio Ultimate to the current version year after year this way.

I wonder if the already upgraded keys attached to Microsoft accounts, that become a bit version fluid, will remain able to use higher versions.