OK, some more suppliers, info.

Found on Lefever damascus barrels, ADH.
ADH was the trade mark of Delvaux-Heuse. This was a joint venture between two powerful companies. Jacques Delvaux and Heuse held a joint patent for the making of damascus, circa 1892.

Thonon
There were at least 20 different Belgian companies that operated under the name Thonon. It was in use from approximately 1836 to 1941. At least one, Fernand Thonon, was the proud distributor of arms to courts of Italy and the court of the Grand Duchy of Luxembourg.

So, I think it might be safe to assume that the Beretta catalog reference to Thonon damascus was produced by Fernand Thonon & Co.

Pete