“Oh,” I said. “Do you mean that if you combine all the medical professionals in those two cities, there’s only one brain surgeon?
“Or do you mean that within the territory that one must traverse to pass from one to the other, there’s only one brain surgeon?”
Turns out, the latter was meant.
Anyway, as with many words that have multiple interpretations or applications, “between” can create confusion.
“Between 2003 and 2004 … ” one might write. Guess what. There is nothing—bupkes—between 2003 and 2004. There’s not an infinitesimal fragment of time there; it’s one year or the other. (It’s even less time than transpires between the end of the Cubs’ spring training and their being mathematically eliminated. Staggering, I know.)
In using that “between 2003 and 2004” construction, you might want to (a) express a time period spanning all or part of those two years, or (b) contrast one year against the other.
If, as in case (b), you’re contrasting the two years, make that clear, too: “In 2004, more than 3,500 bison flew out of the Buffalo airport, contrasted with 2003, when only 1,900 buffalo took wing.”