George, my Erfurt is Sn. 5165. It was the product of the first match up from the shoulder stock exchange. I got the part in trade from Joop VanDeCamp and the first try it slide on very tight. General opinion was that the early guns had hand fitted stock irons so a very high chance that it is the correct one. I have not been able to find any definative answer on the suffix or not on the Erfurts in any refrence books.
http://forum.lugerforum.com/showthre...threadid=11210