AFAIK, you can match keys to the ECU.
The process depends on which Immob system is being used on the car.
VW/Audi didn't stick to a cut off date for all vehicles...
My bosses Audi TT 2002 uses Immob II where as my Audi S8 2001 car uses Immob III.
mmob II
Immob III
Immob IIII
For all of these, you'll need a 4 digit code from the Immobiliser ECU in order to log in and code in new keys.
Note, when you're doing this you need all the keys with you as the old keys get wiped off in the process and need to be re-entered.
MG