I've been playing a similar version of this game for thirty years. You can come close, but, I question ever being able to nail a precise date down.

This would appear to be the oldest gun I've got, at the moment:

[Linked Image from jpgbox.com]

Note that the gun has the 6.5 chamber stamps. Proofed with powder T, for sure later than 1900. I once owned a Darne V20 that was identified as 1910 by the maker. It had 65mm stamps. It was also serial numbered in the 52,000 range, illustrative of a few things. Production was roaring on Darne guns in that era. I've seen few Darne guns of that age with Didier barrels, and I suspect the Darne factory simply out grew their suppliers fairly early on. You will see many old Darne guns with the stamp "Canons Darne" telling you that Darne produced their own tubes. At what point they made that leap I am not positive, but, I suspect prior to 1910. The V20 was clearly marked that way.
Herv Bruchet dated the V20 by comparing the work of the engraver who signed the gun, "Bernaud", with earlier, known examples of his work and a bit of history. Bernaud had to work into his mid 90s, and the later his work was, the worse it got. This was evident on my example.
But, it is the exception in my experience, rather than the rule, that one can nail down a date. No, we can't be sure who stockpiled barrels for French shotguns at the turn of the previous century, producer or manufacturer or, for how long.
The Halifax barrel flats, shown above, are from a pretty old gun. A friend has a Halifax 4, this being a Halifax 3, and the engraving is identicle, which points to his being a later gun, as does his five digit serial number, as opposed to the four digit number on this gun. A call to the factory got him a date of early 1930s, which, seems about right when considering the catalog evidence.
I suppose I'd guess the example Halifax in the photo as between 1905 and 1915. It is an educated guess, but, no more than a guess.
I can't clearly see a way to narrow it down beyond that.


Best,
Ted