On-sale date from the Direct Currents page of From Beyond the Unknown (DC, 1969 series) #8 and from copyright registration.
Writer credit confirmed in letter column of The Unexpected (DC, 1968 series) #126.
Writer and artist credits confirmed in letter column of The Unexpected (DC, 1968 series) #126. The writer is listed in that letter page as Al Case, which is an alias for Murray Boltinoff.
Letters from Tommy Bush, Frank Huver, Beverly Lebenthal, Jerry Wilson, Tony Blizzard, Shane Braun, Leon Drucker and Cherry Holt.
Murray Boltinoff credits Bill Finger, in conjunction with Bob Kane, with the origin of Batman, perhaps the first such reference in a DC comic.