OS reinstallation = reactivation?

[Automan]

Why everytime I reinstall the OS, I must spend an activation?

Actually I still have 7 activation left for my products (FC3, CA & MIG15), but the question is that if I can't deactivate first (like in my case I had 3 total OS crash and was unable to start without reinstall all from my Windows USB image) what can I do to not wipe out an activation?

Keep in mind that I use a separate disk to keep DCS data safe (DCS World folder and Saved game folder are in the 2nd and 3rd disk), no hardware change(except gpu), same cpu, same ram, same hard disk, same OS key e computer name....