I doubt you need codes, these didn't come with any sort of Theft-Loc system like General Motors, Volvos, and Mercedes usually do. Only issue you might have is if your 2001 has the Monsoon system and hers doesn't, or vise versa. Even then the harness is the same for any Volkswagen from 1986-2005.
Vedubya you are the man ! I took the one out of my car and the sticker is in the trunk like you said, After a little search on how to enter the code it was up and playing in her car ! As for getting her old radio out, the left side was being stubborn. Here is what I observed on the radio that I had out of my car. With keys in the slots totally engaged to the point they click - actually releases some of its pressure to the spring clips. I retried the keys in her radio and kept them from just locking in, with that you can apply pressure to the keys toward each door and give the springs an extra bit of leverage. At that point it begged to come out.
I wrote the code from her trunk on the top of her malfunctioning unit and tossed it in my spare parts.