That is great and three cracking Lugers, 39 is a very low number In ref to the brown plastic grips I have come to learn they were made by HK, were they put on a specific series of luger or just a batch within a specific time scale/period?
#39 is the earliest "S-Code" Krieghoff known. The early S codes and the very few G codes had heavy walnut grips. Later S codes had fine checkered brown plastic grips made by Ritzman. In 1936 or 1937 the grips were coarse checkered and then in 1940 they went to black bakelite grips.
Another cracking Luger for my education, again just had a good read of the Lugers at Random book ref these. Not sure how accurate the book is but says these were made mid 1935 - mid 1937, again not many were made. Many thanks for posting this I have learnt yet again