Numbering continues from Billy Bunny (Farrell, 1954 series) [see notes].
The odd numbering is the result of the Black Cobra series continuing the Billy Bunny series, though this connection is obscured by the fact that Black Cobra #1 is not numbered 5, nor does the indicia indicate that Black Cobra continues Billy Bunny. However, Black Cobra #1 is followed by Black Cobra #6 (apparently counting Black Cobra #1 as #5) and makes the connection between the two series explicit in the indicia. The following issue is #3 (again ignoring the connection to Billy Bunny). So the issues were released #1, #6, and then #3.