Transistion period from Assmann production of movements for Gruen to leo Aeby's Madretsch facility and Gruen's plant is unclearly understood. Assmann made U.S. sized movements 16s and 18s until 1905. Aeby started 1904 doing U.S. sizes 0, 6, 12, 16. During this 1900+ time Gruen was setting up their own production. So the first Swiss size Verithins, 17 ligne (.o1" bigger dia. than U.S. 10 size) were very likely by Aeby. His movements are marked Madretsch.
Gruen numbered those 120,000 up. Quit Assmanns at about 68,000. The Gruen Verithin serial numbers started at 450,000. I need to be corrected or confirmed about these numbers. I chose these from watches I have seen. 0 size 1905-7 Mad. 126k shown with 16s 127k. Verithin 21j Mad. 138k, and earliest 16j Verithin Mad. 451920. Seen another with 451880. Madretsch marked watches were supplied until long after1912. I have D. Gruen UtraThin 150080. Do not know who made it. Latest Mad. Verithin I have is 145k. Guessing 1918 for it when 480k was on Gruen Verithins.