The information is from a series of books by Hartmut Thiele called "Grosses Fabrikationbuch Schneider-Kreuznach" which is basically a printed spreadsheet with all of the lenses produced between March 1918 (serial number 21602) and March 1976 (serial number 12 862 325). They are sorted in serial number order which is more or less date order. You get the basic information: name, focal length, aperture, batch size and serial number range and then there are a few columns of extra remarks that may be useful. In this case there is only the word "Muster" (sample/pattern/prototype) in the "customer" column to identify it. Thiele's books are self published and the Schneider ones don't appear to be available anywhere. He has also published similar books on Zeiss, Voigtlander, Rodenstock, Steinheil amongst others.
I don't have much more to add other than there was a previous batch of three prototypes in March 1968 and the first full production batch (200 units) looks to be in June 1971.
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