Post 1964, every Darne was proofed to 18,000. That had actually been going on at the factory for some time before that, 1964 was the year the scribes caught up with the builders and formalized what proof was going to mean going forward. It was considered adequate for guns with 75cm chambers as well.
I'm not sure why anyone would be concerned with proof level on the Darne guns. By law, the proof house in St. Etienne had the highest level for proof in Europe. 15,000 psi was a common pressure for single proof before the year 1900, with powders PJ PM, and especially, PS.

Most of what goes wrong on a Darne was done to it by someone who should have known better.

"Au revoir" works, but the term "Chao" will get you by in France, Spain, and Italy.


Best,
Ted