To me this suggests they had a huge stockpile of war ships going back centuries.
The problem with the Klingons is that they used all of their resources to bolster their military. Little effort was put into scientific research or engineering concepts: this probably explains why Klingon vessels always seemed to be out of date compared to Federation and Romulan vessels of the same era.
That's definitely true, they destroyed their own moon doing it. It looks to me like they were more into upgrading old warships than designing more advanced ships.
But it seems like it works for them- in almost every continuity, they beat the Federation, Romulans and Cardassians.
With their war-like philosophy, they probably made 3 torpedoes for every one the Federation made.
Every now and then they come up with some game changing technology too, like the ship that could fire while cloaked, or that huge Klingon flagship.
My theory with the Cardassians is that they could have been an extremely militarily powerful if they hadn't been so resource deprived, and lagging behind the Federation.
They seem to have a strong sense of infrastructure and manufacturing, but they never had the technology and resources to feed it.