The on sale date is from the publication date as reported to the U.S. Copyright Office in the Catalog of Copyright Entries, Part 2, Periodicals, New Series, Volume 40, January-December 1945, Numbers 1-4. Class B periodical. Copyright registration #B 674693.
Comic itself only lists copyright date of 1944. The December 28, 1944 publication date is what was reported to the U.S. Copyright Office.