If, by "Plume" barrel, one means a swamped rib barrel, 1949 is WAY late in the ballgame for someone to try to take credit for that. Regis Darne had been using swamped ribs for well over 50 years by then, and I'm pretty sure other gunmakers had used the idea also by 1949. I've never seen anyone take credit for that invention, assuming it was a rib choice from way back in the day of French guns.
I have seen stainless steel Charlins (actually "Charlin", as in singular-the Bruchets have one, just the action, that was a display item at the Charlin company before it fell into Darne company hands, that is immersed in a large jar of water) and know that they patented, and built, raised, ventilated ribs for Charlin guns. Not their finest moment, but, the only rib patent I can find exclusive to Charlin.
I'd love to see the evidence of this particular A'bielle gun in photos. I am pretty certain that the guns I have seen had different spelling upon them.
A further point, not really worth anything, is that the photo you provided showing a Darne and a Charlin, Robert (thank you, by the way) is not really illustrating a Darne, per say-it is a clone, based on the early 1894 Regis Darne R model patent, and produced by Francisque Darne, Regis Darne's eldest son.
Note the rocker type safety, located in the base of the action, rather than in the sliding breech, as used by most Darne R model guns produced after 1909.
It's a fine point, but, one that must be understood, when involved in the study of Darne guns.
Best,
Ted
