All I know was that there was no commercial carbine ammo on the U.S. market before c. 1963 because there were NO legal carbines. The Army insisted that none had been released or sold to civilians, and the FBI arrested people who had them for receiving stolen government property. (I don't recall any prosecutions, the government was apparently content to seize the guns.)
Then it was revealed that Benecia Arsenal had sold a few carbines and had NOT recorded the serial numbers. The sale was not authorized, but it was done and could not be undone. So any carbine could, in theory, have been one of those sold, and the arrests stopped abruptly.
Then carbines were released for sale through DCM. At about the same time, the Army was also planning to release M14's for sale through DCM; they would be welded to semi-auto and an "M" stamped after the "M14", making a new model which had never been a machine gun. ATTD had no problems, and the announcement was to be made in the January 1964 Rifleman.
Then came November 22, 1963.