because the Mannlicher Schönauer was an expensive rifle that don't sell by the wagonload I can imagine that this rifle was not in production day by day. probably by using the machinery for everything else
they made a run of the diferent parts from time to time when there was a need again. this parts were laying on stock just taken for the rifles they had an order to complete.
sometimes a part was forgotten and found again in the warehouse after some years.

just a theory