Speaking as a music director myself, does the conductor really count in terms of orchestra size?
At least on Broadway, bigger orchestra shows are always always going to have a "stick" conductor (with actual stick or not), whereas contemporary smaller orchestra shows are often built around the idea of the conductor leading from the piano/keyboard. (In a traditional "stick" show, the conductor is not usually going to be playing any instruments, though there are small exceptions.) So you would count the conductor in a smaller show, as they would also be one of the keyboard players. But, as I said, this would not usually happen with a larger orchestra, so that part of the count wouldn't really have much impact on the numbers, comparatively.
So I would say that, say, if The Music Man is being played by 24 musicians, the orchestra size is 24, even if the very talented Mr. Vaccariello is waving his arms as the 25th person in the pit.