I think that you would want to look into the history of the German "Brown Book" system and the SWF laboratory that later became the IRT. For a long time all types of studio equipment purchased for German public broadcasters were required to be listed in the Brown Book and certified by the central laboratory. This was carried out on two levels: First the types (models) of equipment had to be accepted and listed, and then whenever purchases were made, the actual products were tested by the laboratory and accepted or rejected one by one. This system lasted into the 1970s. The so-called "radio" designations were the ones listed in the Brown Books.
How they came about when they differed from the manufacturer's usual designations for the products involved, I really don't know but would like to know. Complicating the picture are those model designations which were assigned by distributors whose own label had been placed on the product--particularly Telefunken, Siemens, and later Studer--while in most (though certainly not all) cases, the products themselves were entirely the same as the ones available directly from their manufacturers.