Hello @cons,
Yes, you can combine the NOT operator with the IS NULL or IS MISSING operator in a WHERE statement.
I don't see a difference between the tables of WHERE statement operators for SAS 9.2 and SAS 9.4. There can be no doubt that a combination as in
where not (x is null);
is valid. Even the notation
where x is not null;
works and it is mentioned in the section "Use of Indexes" of the WHERE statement documentation of both SAS 9.2 and 9.4 (see links above).