As an unabashed Dallas fan, I have the entire original series and movies on DVD at home and can answer some questions people have asked:
maybe you can answer me this, didn't the cattle barons ball used to be a fancy evening gown and tux kind of thing? I was shocked how casually everyone was dressed.
No. The mainstay of the original series was that they always went to the Oil
Baron's Ball, presumably for the power players in the Big Oil Industry.
Being that neither J.R. or Bobby are part of the oil industry anymore, (yet, anyway, that we know) and Bobby is primarily running Southfork Ranch, it makes sense that they'd be at the Cattle Baron's Ball instead. They never went to a Cattle Baron's Ball on the old show, so we have no frame of reference about what the appropriate attire would be for such an event.