It is locked to the hardware for which you bought the license, not to the OS version.

I have my key since MOS 3.8 if I remember right, and have installed every upgrade released, so 4 times. Always free!

Correction, bought my first key for MOS 3.6 so 6 free upgrades since then.

[ Edited by emeck 17.10.2019 - 22:12 ]