Here is a side by side comparison between my 1917 and my 1937 Brazilian. The 1917 was made in Sep 1918 and based on the 1937's serial number (2080XX) it was made very near the end of the 1917 production run, maybe 1945-46. According to Supica and Nahas there is no meaningful difference between the 1917 and the 1937, the latter just being a portion of the 1917 production run made for a specific customer. According to them the 1937's serial number lies outside the range of those shipped to Brazil, which would explain the gun's apparent lack of import marks. What amazes me (yes, I'm easily amazed) is the lack of any meaningful change between 1918 and 1945.