Serial numbers definitely indicate that they weren't built by Keilwerth.

Keilwerth made at least a couple different versions of the H-Couf Royalist models for Armstrong, but they didn't make all of them. I've seen at least two different models of Grassi horns and I'm sure there are others.

There is a model made immediately after the "Model 28" Royalist that has "Armstrong" engraved on the bell and no mention of H-Couf. These horns have serial numbers that start with 29.

  • s-l1600(9) s-l1600(9)
  • s-l1600(3) s-l1600(3)
  • s-l1600(5) s-l1600(5)
  • s-l1600(4) s-l1600(4)
  • s-l1600(6) s-l1600(6)
  • s-l1600(5) s-l1600(5)
  • s-l1600(2) s-l1600(2)
  • s-l1600(7) s-l1600(7)
  • s-l1600(7) s-l1600(7)
  • s-l1600(9) s-l1600(9)
  • s-l1600(1) s-l1600(1)
  • s-l1600(1) s-l1600(1)
  • s-l1600(8) s-l1600(8)
  • s-l1600(10) s-l1600(10)