SMG-
I think you are technically correct, regarding the HSCA.
Later, in one of the many JFKA conferences, Blakey said he did not know where the shot from the GK went...so I deduce Blakey thought there had been a shot from the GK.
I think there was a gunshot at the GK during the JFKA, resulting in the smoke-and-bang show.
I don't know where the bullet went either.