If you want to skip a line by a variable that is not one of your column variables (COLVARS), the best way is to use the ALTSORT parameter since any variable in ALTSORT can be used as a SKIPLINE and NOSPLIT parameter. (Avoid using HIDVAR in the future.)
Example:
COLVARS=<.param> var1 var2,
ALTSORT=grp param,
SKIPLINE=grp,
Example:
COLVARS=<.param> var1 var2,
ALTSORT=grp param,
SKIPLINE=grp,