One factor that is also not considered is that from 2750 until the outbreak of the 1st SW in 2786, there was 36 years in which to go batshit insane on the whole ship building front, especially so when the advantage of a large fleet was shown by the SLDF's massive fleet peacekeeping deployments.
Naval infrastructure existed to an large extent in that era and even if for the first 10 years (2750-2760), production was low, as new yards were commissioned, twenty six years of rapid building programs and the return of mothballed ships to the fleets, perhaps added to FirstStarLord’s thought on the bandit fleets, would lead to massive numbers of ships.
For example, the USN, once it got its naval yards cranking in the period from 1942-1945 added 78 major fleet vessels (cruiser or larger) to the rolls, which with pre-war totals (including losses) was 137 ships. These numbers are a good match for BT fleet numbers.
The numbers of the house militaries doubling and doubling again seem to point more at the regiments than the shipping, at least in my view. Ship numbers in the first jump go from 155 to 239, but a true double would be 300+, which would point to a 600+ final figure, not the lower 475+ by a second doubling.
I think what we will see, in order to match existing fluff, is that the expansion of the House Navies in the period from 2765 to 2786 will be an ever increasing rate of WarShip production where fleets of each nation will be 150-200 strong.
At least that is my view.