Strange that double triggers are not listed as an option. Also "not available without rib". Both options were available at some time, but I don't know when.
I can't tell when the ad was published.
It states in the description that the standard includes the twin single trigger is standard. That seems to be what your gun is equipped with. From the ad pictures and description I would say your gun is a standard model consistent with the time of the ad.
It may be that the twin single standard was changed to a straight double trigger at some point. I own several double trigger O/U's because I find them unique and match most of my doubles. I recently bid on a 1950ish that looked a lot like this because it had double triggers. It was advertised as such, but for all I know (and likely the dealer) it could have been the twin singles. A lot of people could own such a gun and maybe never know it.
