The "3jf" simply implies color code = 3 (green) and the jf is meant for the Japanese market. The multiband 6 is on the OTHER side of the name. Casio uses "Waveceptor" name for Multi - Band anything and they will stick a "W" somewhere in the prefix for designation. In this case: GXW-56KG-3.
The prefix " DW " came out long before the atomic G's, so the naming convention does not apply in those cases.
sent with aloha