Might be any Klingon ship starts out fairly plain, and then endures through centuries of refits, accruing Gothic ornamentation among other things. And any fresh start thus goes back to the roots and involves a fairly plain design that gets mass-produced - and in a war where losses mount, it's these fresh ships being lost, before they have time to collect fame and hood ornaments.
Timo Saloniemi
Makes sense.
From the fact Tkinga and berels are seen over 100 years after they originally appears shows that Klingon ships are made to last and be continually refited and upgraded.
My guess is that the houses treat their fleets like family airlooms and signs of prestige and very carefully maintain, upgrade and modify them from base designs.
I would go as far as saying every house even has it's own fleet doctrines with some houses relieing on fast raiding and others heavy hitting battleships.
In later trek although the the houses still have their own fleets my guess is that the Klingon defence force refers to the fleet or fleets directly under the chancellor's control and as such will likely be more standised.