Reprogramming remote key - question

Hello

I have an Octavia 2 (2006) with one fully working remote key fob and one which starts the car but does not operate the central locking.

I see various sets of instructions on the web about how to reprogram the non-working fob eg. https://www.programyourkeys.com/Program_Car_Keys_-_Skoda.html
 

Assuming these instructions are correct - and hopefully someone here can confirm?...I have a question about the procedure.

Is it necessary to wipe both remotes (including the working one) and re-program them again?
Can just one remote be re-programmed without affecting the operation of the other?

The instructions at the URL above suggest that each remote has its own program:

"...When performing programming on additional remotes the procedure is the same, except you press the unlock button 2, 3 or 4 times for the different remote."

...so how do you know which of the 4 slots the currently working remote occupies?

Or have I completely misunderstood the whole thing?!  Hopefully there will be many people on here who have gone through this.