Can I virtualize a retail copy of Windows 7 on a different machine than I originally installed it on now that it's Win 10?

Question

I have two PCs. For the first, which was blank, I bought a retail copy of Windows 7 Home Premium and installed it a few years ago. Then, when the Windows 10 free upgrade was announced, I waited a few months before upgrading it to Windows 10. I just checked, and that PC's Windows 10 doesn't use the same product key as was used for the Windows 7 install. My second computer came with Windows 8 and was also upgraded to Windows 10. I'd like to virtualize Windows 7 on my second PC, probably with VirtualBox, and I know that virtualized Windows needs a product key like any other version of Windows. Since my first PC was upgraded to 10 and is no longer using that product key, does putting the retail copy of Windows 7 that was on there into a virtual machine on my second PC count as a license transfer?

Research: This SuperUser blog post from 2011 says I get one transfer as long as I remove the software. I know that OEM versions of Windows are tied to their machine, but I used a retail version: http://blog.superuser.com/2011/04/06/microsoft-licencing-transferring-windows-to-another-computer/

This is the latest version of the license (I filled the correct information into the tool and it gave me a PDF), which seems to say that I get unlimited transfers. It also mentions that if I virtualize the OS, it can't be physically installed to a machine: https://www.microsoft.com/en-us/useterms

More SuperUser posts that are relevant but don't quite answer my question: Does the license allow me to run Windows 7 in a virtual machine and on the host?

How does Windows 7 licensing work for running the OS as Virtual Machines?

This website says that I can virtualize my old copy of Windows if the PC is now using 10. However, does virtualizing the old Windows 7 on a different PC than it was originally on count as a license transfer?: https://www.infopackets.com/news/9613/windows-10-upgrade-can-i-keep-my-old-windows-install

Answer 1

The Windows 10 upgrade is presently free, or when the promotion is over, heavily discounted for users of a previous version of the operating system. For this reason, qualification for an upgrade is contingent on the existence of a valid license that's being replaced.

When upgrading the retail Windows 7 install on your originally blank PC, the Windows 10 license became tied to that Windows 7 license.

You can install Windows 7 virtualized on your other PC and use the product key from that retail purchase -- so long as you uninstall Windows 10 from the original PC -- since that Windows 10 install is tied to that Windows 7 retail license by way of upgrade. You also can't install that same license of Windows 7 on the original PC either.

In other words, upgrading Windows 7 to Windows 10 does not free that Windows 7 license for reuse. That Windows 7 license effectively does not exist so long as the Windows 10 that upgraded it is in use.