It could be that rather than the entire Klingon Empire going to war over Khitomer or Narendra, only particular houses that were directly harmed went to war with the Romulans. There's no reason to think that the entire Empire would want to fight over the destruction of a couple of colonies. And the larger noble families probably have their own warships, and wouldn't feel the need to wait for the Chancellor's approval to fight. So history from the Federation perspective would record that the Klingon political entity did nothing in response to Khitomer and/or Narendra, but looking more closely, we'd see that a de facto
state of war existed.