The catalogues never have the bracelet codes unfortunately, it's the price lists we can sometimes find that info in.

It quite possibly is the case that there are different bracelets for the .511 and the .523. The join between the watch head and the first link in that flat link bracelet strikes me as clumsy though and I wonder why they would select a different bracelet for the steel watch when they have one with a much more harmonious transition on the PVD watch. The PVD bracelet is clearly designed for the watch, the rectangular steel one less so, to my eyes anyway. Though variants of that bracelet are on contemporary Regattas too, so arguable which watch it is originally designed for.

The bracelet it's on in the 1983 catalogue does look more "bespoke":

but as you say, some of the detailing on that watch isn't final anyway. Looks like they might have originally intended to be 100m waterproof with mineral glass, but by the time they become a production reality, the depth rating had dropped to 30m and they all sport plexiglass.

Could be any number of reasons why that pictured bracelet doesn't seem to appear so much in the wild; supplier issues, demand, supplier relations, who knows. It's something I'll keep an eye out for when I'm looking at 5100 Carreras from now on, for sure!