Product code duplicating

I have several Windows 7 computers which I am upgrading to Windows 10. I have Windows 10 on disc.

I use Speccy to look at the Serial Number/Product Code. It doesn't matter what computer I upgrade, or if it is an Upgrade or a clean install, I end up with the Product Code being the same on all the Windows 10 computers. I am 100% certain that I did not enter the Product Code on any computers except the first one, which happened to be my daughter's computer. It is that Product Code which is showing on all subsequent installs. It doesn't matter if I use my disc or if I download from Microsoft.

Logically, it cannot be an error on Speccy's reporting.

I can't understand how this could be happening. Also, I am concerned that MS could look at my computers and say the computers have to have unique Product Codes. They did, but not now.

Can someone explain what is going on?

First of all, are you talking about Product Keys? If you upgraded to Windows 10 from Windows 7/8/8.1 every upgrade gets the same Product Key, the generic product key for that version of Windows. Every Windows 10 Home from an upgrade will get the same generic product key. Every Windows 10 Pro from an upgrade will get the same generic product key, etc.

Your entitlement/license for Windows is based upon the Installation ID and the Product Key is only one element of the Installation ID. The Installation ID is a combination of the Hardware ID - which uniquely identifies your computer based on motherboard information, the Product ID - which identifies which version of Windows you have installed, and the Product Key - which identifies the basis for activating Windows (Retail, OEM, Upgrade, Volume License, etc.).

It is the Hardware ID that identifies each unique computer, not the product key - and that makes the Installation ID unique to each computer even thought the version of Windows 10 is the same (Product ID) and the basis for Windows activation is the same (Product Key indicating an upgrade).

If you do a clean install on the same computer after an upgrade - Windows 10 will calculate the same Hardware ID if the motherboard is the same, the Product ID will be the same if you installed the same version of Windows 10, and if you skip entering a Product Key then the same generic product key will automatically be used. This results in the same Installation ID for that computer which is then sent to Microsoft activation servers. Since that Installation ID was previously saved there during first upgrade process, the digital entitlement/license for Windows 10 for that computer will be retrieved and the activation server will send back the code for Windows 10 to activate itself.

This is why your Windows 7/8/8.1 product key is unaffected by the upgrade to Windows 10 - because the Windows 10 activation from an upgrade uses the generic Windows 10 product key - not the Windows 7/8/8.1 product key - to calculate the Installation ID.