Windows 10: How can I tell if I have used my one transfer of Windows 10 "Retail license"?

I have a retail Windows 10 Pro license.And I have read: Note that retail license users who upgraded from Windows 8.1/8/7 to Windows 10, have only one time transfer ability for their Windows license." The original terms of the free upgrade were that the upgrade to 10 was free for the life of the device. This is similar to the OEM restrictions.I have during the life of the PC changed the NIC and at another time I changed to boot drive via cloning from an HDD to an SSD. I don't have a copy of the key anymore but gather that there is software I can purchase that will expose the key. BUT will it w

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Building a new rig to transfer Windows 10 but not sure if it's OEM or Retail

If you upgraded from a retail box copy Windows 7, it has retail transfer rights.

Use the following to see if you can find the original Windows 7 key. If you can't find the original Windows 7 key, you won't be able to transfer it.

Step 1: How to Find Your Product Key After Upgrading to Windows 10

Step 2:

• How to Transfer your Windows 10 License to a New Computer

 

Windows 10 license transfer

If its a retail license, yes, you can transfer it. Learn more about transferring the license:

• How to Transfer your Windows 10 License to a New Computer

 

Windows 10 upgrade license

The interesting question is that: the upgrade takes place before 29 of July. If I upgrade the PC (change the MB), and I transfer the Win 8.1 license to this new PC (cause 8.1 is retail FPP), will I be able to upgrade to Windows 10 for free? Or a upgrade license must be bought?