Děkujeme jspcal za odkaz, který inspiroval tuto odpověď.
Funguje to s
CREATE OR REPLACE PROCEDURE FILL_DATE_GAP AS
BEGIN
INSERT INTO DUMMY_DATES
SELECT to_date(add_months(date '2015-01-01', level - 1), 'yyyy-mm-dd') mth,
'V'
FROM DUAL
connect by level <= 14
MINUS
SELECT DT,
FLAG
FROM DUMMY_DATES;
END FILL_DATE_GAP;