thanks,
2), 3), 4) seem to be explained and all look like standard 5x5 alphanumerics with - in between.
1) Appears under "Windows activation" on the system properties screen and takes the form (different digits)
Product ID: 12345-OEM-1234567-12345

So based on your descriptions maybe 1) and 3) uniquely define my particular PC from the 1000's of PCs that the OEM uses 3) alone for.

Then the COA key 2) is the legal entitlement I have with MS and has nothing to do with the OEM.