ar44 coded K98k made in 1944.  The receiver on this rifle was made by Mauser Borsigwalde (Berlin) but then sent to Mauser Oberndorf for assembly.  The stamped sheet metal trigger guard group was made by Mauser Oberndorf (byf code).  You can see numerous E/135 waffenamts indicating work by Mauser Oberndorf.   When "Backbone of the Wehrmacht" by Richard Law was written, this example was reported as the highest serial number known for the code and date.