I do not collect K98's, although I know that Simson made them in WW1. I know they reworked many carbines and rifles after 1918, but that is about it.
One of our sources was a translation from a german magazine (the author of the article gave us permission to use sections; the others were from the city of Suhl, and the book Simson Legende, both translated from German and just used as sources of basic information. Graham traveled to Suhl Germany in October and met several folks that helped us out.
As you said, cross traveling for info is good to do. I have checked around for MG Simson owners, had no luck. Have received almost the same amount of info on K98 / rifles (a bit, but not much).
There reall is so much, *not* known about Simson. I am sure more information will come to light in the next couple of years
Ed