When Contax and Yashica began their partnership, prototypes were made in Germany. Even with the RTS, some AE lenses were made in Japan. Special order lenses, along with others in the line continued to be made in Germany also. I have a 50 1.7 AE made in Japan.
With the advent of the MM lenses, many were made in Japan.
The Zeiss website explained, maybe a year ago, that it was a matter of economics. Hence, MM lenses now can be found made in Germany also.
I have one from german production, the 1,4/85 (MM); all the others (1,4/50 AE, 2,8/35 AE, 2,8/28 AE, 2,8/135 AE) are from Japan. I assume it's just a matter of factory capacity: the more common lenses are mostly from Japan, the less common lenses from Germany.
Hi: i have also contax 50/1.7 AE lens with serial #6516585 made in japan and perhaps many techanicians made experiments on it and purchased here on 7-2-2004 Lahore, Pakistan.Performance wise it is good.