The last three COUNT functions use CASE expressions to count the occurrences of the three notations for missing values. 
   count(case
            when &col=.n  then put(&col, 2.)
            end) "Coded as NO ANSWER for &col",
   count(case
            when &col=.x  then put(&col, 2.)
            end) "Coded as NOT VALID answers for &col",
   count(case
            when &col=.  then put(&col, 1.)
            end) "Data Entry Errors for &col"
%mend;