Personally, I believe the K't'inga was an upgraded version of the earlier D-7, similar to the Constitution refit seen in TMP. You know, the Klingons wanting to maintain tech parity with Star Fleet. BTW, I've seen the D-7 also called Klolode. Maybe it's a matter of the earlier ship being a D-7 Klolode and the refit being D-7 K't'inga?
Just to mess things up, I'll also throw out the idea of the ship being just like the Klingons themselves in TMP.
In other words, we know what TOS Klingons looked like and TMP showed us new Klingons and GR wanted us to think, yeah, this is what Klingons looked like all along.
Maybe it was the same with their ship. Sure we saw the Klingon warship in TOS and then a new one in TMP. Maybe it was the same thing with, yeah this is what the ship always looked like, never mind the differences.