Hi Paulokello1,
I am Dave, an Independent Advisor, I will help you with this.
Yes your understanding if the process is perfectly correct.
If you purchase the Pro upgrade licence for approx. $99 by clicking 'Go to the Store' on the activation page in the Settings App, that Pro licence then inherits the status of the underlying Home licence.
So if the Home licence is OEM (pre-installed) then the Pro licence inherits that and is not transferable, if the underlying licence is retail, then so is the Pro licence and that is transferable.
if your Windows 10 is Home and pre-installed, while a full Pro licence is dearer than the upgrade licence, in the long run it is a better option than the Pro upgrade licence.