I am using a 12/24 that seems to be a K7F2 (scale in meters and feet, no half moon below scissor strap lug, 12/24 counter switch installed). It does however have a serial number below 2,451,850 -- which would make it a K7F, according to the Ian Parker Guide and according to the Rollei Club web site. Perhaps it is a kind of Frankencamera, built from parts of both models.
When shooting 220 film, it is **NOT** necessary, on the camera I am using, to press the shutter button an extra time. After the twelfth shot and before winding on, you just turn the 12/24 selector switch to '12' (having started the roll with the switch set to '24', obviously). Before the switch is even turned all the way round, you immediately hear a very obvious, solid click and the counter resets from displaying '12' to displaying '0'. You then wind on, the counter shows '1', as you would expect, and you are ready to shoot the second 12 frames.