In my experience my OEM "sticker" or COA as it is called did not match the retrieved W & key and failed to activate when I tried a clean install.
My research found the following guide which provided my solution :
How to do a clean W 10 install for OEM Windows installs :
The Win7 OEM key built in to the firmware of your (or indeed anyone’s) device will never match the key on the CoA sticker.
This is a peculiarity of older Windows activation methods such as that used in 7.
Key in the firmware is a generic key for the brand of your device, Dell, HP, Acer, etc. and version that has been supplied for said device, whether Win7 Home, Pro, Ultimate.
Key on the CoA is unique to your device, but it is not used from the factory. It is only supplied as a legal requirement.
In Windows 7, OEM Windows devices (I.e. big name brands like Dell, not home built PCs made by buying individual components yourself, as many of us also do) use the generic key from the firmware (BIOS) of the device, which is validated against an OEM.xrm-ms certificate that is part of the Windows system files installed from a Windows 7 OEM install dvd.
Windows 7 OEM dvds for the various OEM brands contain the certificates needed for that brand. A Dell disc, for example, will install on, again for example, a HP computer, but it will not give you an activated system, because the Dell cert and the HP firmware key won’t match.
If you currently have a Windows 7 install that is activated and working (I mean working other than refusing to upgrade to Windows 10 from Windows Update) then I would recommend that you also Google about the following. I have tried to explain as best I can, but hopefully it points you on the right track to research what I speak of before doing it, just to reassure yourself and learn what’s involved.
(This I should point out is completely legit method, not piracy in any way. You will be using Microsoft tools to do this, and you are entitled to this licence if you have a legit Windows 7.)
Get Microsoft Windows 10 media creation tool. A small app to download, this will allow you to get an install ISO of Win10 that you can burn to a DVD and use. Or you can if you know how use a USB key. (Learn about an app called Rufus if you want to use a USB. You’ll need it to make an install USB)
If you currently have Win7 home basic or home premium, then get Win 10 home ISO. If you have Win7 Professional or Ultimate then get Win10 Pro.
On a Windows 10 install disc there is a file that may be used to generate an activation file from your valid Win7 install which can then be used to permanently activate a corresponding, cleanly installed Win10 install on the same machine, without any need to go through the upgrading from Windows 7 rigmarole.
The file is named “gatherosstate.exe” and it is contained in the sources folder of any Windows 10 install disc.
Windows 10 activation is different to Windows 7, the branding of your machine won’t matter here, this is a generic method.
If you copy this file to a folder on your pc, (anywhere on the hard drive, but make sure it is the only file in the folder). Run the file and it will create a XML file “GenuineTicket.xml”, which you should save to some place safe like on a memory stick, as you’ll need to use it later to activate 10. (Clean install will wipe the hard drive/SSD of your computer.)
The rest of the instructions I will just copy/paste from another site
Quote:
This can also circumvents the "Something happened, Windows 10 installation has failed" error while upgrading.
Preconditions:
You have Windows 7 SP1 or Windows 8.x activated successfully (retail or OEM licensing only). This doesn't apply to volume licenses such as KMS or MAK.
Download the Windows 10 ISO that's suitable for the upgrade path I.e. Windows 7 Ultimate or Pro will upgrade to Windows 10 Pro.
Instructions:
Optional: Validate your copy of Windows 7 SP1 or Windows 8.x
Install all necessary drivers e.g. ethernet & wireless card
Open your Windows 10 ISO and extract gatherosstate.exe from the sources folder to your desktop
Run gatherosstate.exe and wait for the GenuineTicket.xml file to be created
Copy the GenuineTicket.xml to a USB thumb drive or something
Boot to your Windows 10 USB or DVD and perform a fresh install
Disable your internet connection
Copy GenuineTicket.xml to C:\ProgramData\Microsoft\Windows\ClipSVC\GenuineTicket\ and then reboot
Connect online and you should be activated
If you ever perform a clean install in the future simply select "I don't have a product key" and then when you connect online Windows will activate itself.
If you can’t see the “Program Data” folder after installing 10, go into folder options in the Windows file explorer and tick show hidden files and folders, as it is by default hidden.
This is a working solution.