keyless entry remote question
 

Curious...
If you get a used car that has keyless entry and it is missing the remote
(key fob)..
You buy a replacement remote and program it...
If someone else has the original ..would it still unlock the vehicle if a
replacement has been newly programmed?

Been reading that most, if not all, remotes have to be programmed at the
same time..
So if you program a new/replacement remote...the original shouldn't work?
(unless programmed at same time)
Is this correct?