Rod, I researched the question and wrote an article a while back that was published in our Chapter #168 journal The Torsion Times. Long story short, there was only ONE maker of 400-Day clocks who routinely stamped "Made in West Germany" on their clocks made after WWII (Kieninger & Obergfell, aka Kundo), and did so from 1950 to about 1975. Further, there was no legal or customs requirement to use "Made in West Germany" on anything, although there WAS (and still is) a requirement to stamp the country of origin on imported goods to the U.S. and many other countries.
We don't know the reason why Kundo did that, since it was not a customs requirement and with only one known exception NONE of the other German makers did that on their clocks made after WWII. That includes Aug. Schatz, Kern & Söhne, J. Link & Co, U. Herr, M. Reiner, U. Neueck, Georg Würthner, Edgar Henn, Sigfried Haller, Konrad Mauch, Franz Hermle. The exception was Schatz, who "did" stamp "Made in West Germany" on one model which they made for the H. Coehler Co., but not on any other clocks they made.
One thing that will cause some confusion on this is that Kundo made a LOT of clocks for traders and put their names on them, including the Cuckoo Clock Co, Forestville Clock Co, Fred J. Koch, Euramca Trading Co, DeBruce Watch Co, H. Coehler Co, Perfecta Watch Co, P.R. Myers & Co, Rensie Watch Co, Royce Watch Co, J. L. Hudson Co, and Welby Corporation. All of those made by Kundo between 1950 and 1975 will be stamped "Made in West Germany", but there are also many that were made for some of these same traders by other makers which were stamped only with "Germany" or "Made in Germany".
In summary . . it was NOT a requirement to stamp "Made in West Germany" on anything after WWII, although there were a lot of companies who did for other types of goods such as small home appliances. It WAS a requirement (and still is) that the country of origin be stamped on imported goods to the U.S. and to most other countries.
Hope this will help you win your argument!
John Hubby, Secretary
The International 400-Day Clock Chapter #168