Thanks for the lead. A copy of J-C Mournetas, Les fusils de chasse de Regis Darne, 2nd edition of 2006 arrived via FedEx today from France. It's full of the Darne patents and a huge amount of Darne lore.
Just a note on the author's failure to draw up a table of serial numbers: (free translation here) "...I so much wanted to find the key to this (serial number) enigma and to be able to, as for the IDEAL, offer to all lovers of fine arms, a precise chronology by serial number. Alas, the greatest part of the documents have disappeared. Moreover, the principle of deciding serial numbers of Darne guns is so bizzare that it's impossible to sort it out." He goes on to note that guns of different types are found with the same serial numbers, observing that such might cause concern with the police!
Regards, Tim
