I removed the following speculation from the background section:
- A number of explanations are possible for this apparent inconsistency. Klingons might use the word "sister ship" to include all battle cruiser types. There could have been two different vessels with the name Klothos commanded by Kor, just as James Kirk commanded two ships named Enterprise. So this Klothos might have been the D7-class successor sister ship to Kuri's battle cruiser. D5 might also be a 23rd century designation for a variant of the D7-class. So Kuri's ship could also be a D5-class ship. Or, as the senility of Kor was the key focus of the DS9 episode's plot, he might have simply been confused with the class name of these old ships. The lack of canonicity of TAS may also be to blame, as the writers would not have been beholden to it.