I cvannot answer your questions, but interesting read about Glass, cheers!
Anton Fokker is credited with inventing the Interruptor Gear so bullets could be fired through the arc of a propeller, but I believe Euler in 1910 and Roland Garros had already invented previous less good devices like deflector plates mounted on props, but they could be very dangerous...sometimes the bullet ricocheted straight back into the pilot's face, and this did not do the bullet any favours at all.
Various other mechanisms were used, but I think the Wiki article mention of "through the propeller" might be referring to one type in which the bullets were fired through a hollow prop shaft, but I don't know any more about that type.