Plus in the 80's and 90's many of the TOS books were written with the idea that TMP occurred 6 years after "Turnabout Intruder" and that Kirk had commanded the Enterprise on a second five-year mission. (Or, actually there is still enough space for a second five year mission, since I was checking Memory-Alpha and aside from the 2270's, there is nothing much else dating it's time period, except that it couldn't have been later than 2278, due to the Bozeman's crew wearing the red uniforms in Cause and effect, and no earlier than 2273, as Icheb establishes Kirk's first mission ending in 2270, and both Scotty and Kirk's lines in the film indicating that it had taken 2.5 years for the major overhaul to occur, so a second five year mission could've occurred between late-2270 and 2275.)