Indicia date is Fall 1979, date on cover is November.
Cover is dated November, the same as DC Special Series #18.
On sale date from the 1979 Library of Congress copyright records (
cocatalog.loc.gov). Date given as July 5 in Comics Journal #47, DC Coming Attractions #32, and in a house ad in Weird War Tales #80. Date given as July 3 in Comic Reader #170.