You are correct in that the VIN or build label under the dash (fuse box area) has the "Alignment Group" listed on it. If your 2001 GLS label is similar to that on my 2003 MV, the alignment group is listed on the same line as "GLS" would be.
If what you are saying is that you can't find the VIN / build label, also look in your owner's manual in the front of the "Maintenance" booklet. If no luck, contact VW of America.
Since the 2001 GLS has the same wheel and tire combination and (I think) springs as my 2003 MVWK, the alignment specification is probably the same. Mine is on the label as "K5", which means Alignment Group 5.
Maybe other 2001-2003 GLS owners can look at their label and advise.