Shotgun lover,
Not ALL Darnes were built sans lower rib-you could get them how you wanted them, at all points in the history of the company. I'm guessing few people ever went to the trouble to order a fitted Darne, based on used guns I see, at least in the USA, at any rate. During the 50s, 60s and 70s, the people that ran the company did attempt to ramp up production to keep guns in inventory for stocking dealers, a disaster as far as I am concerned, with a design that is as fit critical as a Darne.
It is when someone attempts to use a non-fitting Darne we get the ignorant comments like "Darnes stink". There is precious little one can do to get a Darne to fit better, as the steel rod in the wrist doesn't allow for adjusting bend.
My 12 has an under rib, and I suspect the gun was built for export, and not a custom order, as it is marked "Made in France" in English, on the top rib, and I believe the under rib was put there to help keep the gun from feeling "whippy" with the 26" barrels it was built with. A fact not often mentioned is the good handling and balance requirements of any given gun are going to be different depending on the human expected to use the gun-my ideal will no doubt be a bit different than your own.
What Gough Thomas said about the Darne, in the era he said it, in the country and to the people he said it to, borders on courageous. He would have been roundly criticized by those he knew for mentioning anything from France as having any improved qualities worth considering.
But, he did. For good reason.
Best,
Ted