See Crunch Automation basics for more information.
The SET MISSING command allows you to change whether a category is set to be “missing” and excluded from the base of percentages. When used on multiple variables, all should have the exact same categories (in number and codes). The changes will happen in place on the same variable.
SET [NOT] MISSING code|"label", ..., code|"label" IN alias, ..., alias;
SET MISSING 98, 99 IN Age, Gender; SET NOT MISSING 1, 2 IN Age, Gender; SET MISSING "Not Asked", "NA" IN Age, Gender; SET NOT MISSING "Yes", "No" IN Age, Gender;