I seldom if ever booted the Windows 7 Pro and had even removed the Windows sticker from the casing and replaced it with a Free Software Foundation GPL sticker so I wondered if I might need the product ID number for the update. I was also a bit concerned lest the update messed things up because I also multi boot Debian along with FreeBSD, OpenBSD which I also haven't booted for a long time.
The update was long and boring and after the second reboot before proceeding with the numerous updates I booted Debian and ran update-grub and Windows 10 appeared in the boot menu and after several more reboots the process was completed and fortunately I didn't need the sticker with the productID which, as a precaution, I had looked for and found in the registry.
I might mention that I didn't bother to make any backups. If the update had gone wrong then I thought—to hell with it!—I would have simply deleted the partition because there are better ways to spend one's free time.
