Note there is a variation of the SELECT statement where you are not restricted to one single variable or expression that is tested against a series of values, but where you can use as many expressions as there are WHEN clauses. In the example below there are 3 different clauses: one for the first day of a month, one for the months Jan, Apr, Jul and Oct, an one for februrary 29. If none of these conditions is true, the OTHERWISE clause will be executed.

SELECT; /* no variable or expression here !!! */
WHEN (Day (Date) eq 1) Do; ... ; End;
WHEN (Month (Date) in (1, 4, 7, 10)) Do; ... ; End;
WHEN (Month (Date) eq 2 and Day (Date) eq 29) Do; ... ; End;
OTHERWISE Do; ... ; End;
END;

Note however that the second clause (Jan, Apr, Jul, Oct) will not be executed on the first day of these months, as the first clause already processes the observation.