We saw schematics of a Klingon battlecruiser on the briefing room screen in either "The Enterprise Incident" or "Day of the Dove". Considering we "first" saw the D7/K'tinga battlecruiser (in-universe) over 100 years earlier in ENT: "Unexpected", I would expect 23rd century Starfleet to have aquired quite a bit of info on them.
But to be honest, Trek is rife with inconsistancies about Klingons. In STVI, Uhura didn't speak Klingon and McCoy didn't know anything about Klingon anatomy. You'd really expect them to know more about their arch nemesis.
But to be honest, Trek is rife with inconsistancies about Klingons. In STVI, Uhura didn't speak Klingon and McCoy didn't know anything about Klingon anatomy. You'd really expect them to know more about their arch nemesis.