The Kodak Recomar 9x12 holders are common in the US and they often come with the film adaptors, but in Europe the plate holders & film pack backs seem to have bee more prevalent.

I have detailed photographs of the Kodak holders & inserts, they were made to be used together and the inserts are different to those made in Europe. By the time Kodak entered the 9x12 market buying Nagel the field was already fairly mature and glass plates far less common so there was then a greater need for a dual purpose plate/film holder.

The simpler European style film inserts work fine and are obviously far easier to make, the costs of getting a pair of dies made to press Kodak style inserts is to high for the small number required, particularly for more than one size.