There are definitely some airports whose name includes the "International" (San Francisco, Dayton, Dallas Ft Worth) that don't get the Intl appellation on the BP. This is why I speculated it might have to do with length. Though on the other hand, Dayton is certainly short enough that Intl could fit. I suspect it's just inconsistency in how they were entered into Sabre's database.

Incidentally, in theory, could an airport have flights from Canada and no immigration/customs (due to the pre-clearing)? If so, could such an airport use the "International" designation?