According to Dr Samuel j Newland, Professor, US Army War College, in his on-line article, The Forgotten Giant, A brief look at military Small Arms production at Steyr, 1864-1900, footnote 25
"In 1945, the Russians took or destroyed most of the production records"
Steyr came within the US Army occupation zone.

I have ordered a 2010 book in German, Josef Werndl und die Waffenfabrik in Steyr, which may have more information on pre-1945 historical records.