In the spanish language track the line ends with, "....senor D'Amato."
In Spanish, Senor can
mean "sir," but it can also mean mister, depending on how it's being used.
or perhaps the 23rd century knig of ... Italy had knighted D'Amato!
An interesting possibility. Kirk does refer to ambassadors by their job position, to McCoy by his occupation. In the future miss and mrs. have returned to common use, and Kirk uses them both.
If D'Amato were to have been knighted at some point in his past, would Kirk on occasion use that title in referring to D'Amato?
As opposed to employing "Mister?"