That is the hallmark of a Halifax. Brazed barrels. As to the specifics of why Mr. Darne was awarded his patent in 1902 for the fretted barrel, or monoblock, after Pieper had a previous, similar patent, I can't say, however, I can say that Regis Darne took it and made it a wildly sucessful innovation.
What did Pieper do?
Twisted barrels were not used in France for 3 or 4 decades after Pieper's patent. They took to steel tubes from the onset.
Best,
Ted