This may or may not be your answer, but on an 8x56 Mannlicher-Schönauer made in 1925, the number
A-1525 has been engraved on the scope body and also the trigger guard. This is in addition to the usual Steyr factory serial number. The worn out leather sling on this rifle was marked S. L. Rohu, Gunmaker, Sydney, so I assume it had spent most of it's life in Australia. What I also assume is that, at some time the Australian government had some bright idea of trying to stamp individual numbers on firearms with a view to registering them. If that's the case, it might explain the number on yours. However, I'm not too sure what a "knox form" is in front of the chamber.