All you need is your POP ID number. In fact, even if you forget your number and lose your card, if you've played in a TOs event, chances are they will be able to look up your number in their player database. Getting a new number should only be done as a last resort, in cases where there is no way to find your original number. Using only one POP ID keeps all your participation records in one place and gets you maximum credit for things like player rewards.
BDS