According "The Undiscovered Country", "70 years of unremitting hostility with the Klingons" were about to come to an end. So that would put a potential Klingon conflict 20 years prior to Donatu-5 if TUC occurred in the mid-2290s.
Just so we're clear, the hostilities started 20 years prior to Donatu V and continued up until TUC, correct? So Donatu V would have been part of that hostile period, since "unremitting" means "never slackening or stopping; unceasing; constant". Which doesn't take into account the enforced peace of the Organian Peace Treaty in 2267, of course ;-/
I find it hard to beleive that the Federation was in a constant state of war for 70 years, since the Enterprise, the pride of Starfleet, saw relatively little action against the Klingons. so I guess the idea of the Cold War with various flareups makes the most sense.
Well even during the Organian Peace Treaty the Klingons were still...
- Poisoning grain supplies ("Trouble with Tribbles")
- Sabotaging the Enterprise's warp engines to make it look like an accident and then decided to just outright attack the ship. ("Elaan of Troyius")
- Sneaking across the neutral zone to destroy the Grissom and attack the Enterprise ("The Search for Spock"). (When did the Organian treaty end anyway?
)
And that's the incidents that we're aware of...
From the Federation's POV, it probably was "unremitting" and "hostile"...


Yeah. No axe to grind from me either. Just wanted to throw out other data points. I think as others have said, those TOS dates and descriptions are specific enough to be interesting but vague enough to be anything 
