Variables shouldn't be used at all in the record selection formulas, do you mean values?
A {table.field} in ["A","B"] is not using any variables, it is a hard coded list of values compared to a field, and I doubt that you'll find a small quantity available, although the version of your software and memory will certainly change this.
If you have that many, a not({table.value} in ["X","Y","Z"]) might be simpler to code, or use a like operator.
If you post:
Crystal version
Database/connectivity
Example data
Expected output
You might discover that someone has another idea that will serve you better.
-k