No. That only applies to C-store ships that have fleet versions.
The fleet modules are pretty over priced any way by my current understanding, they buy an individual ship for a given character, they don't unlock it for your account. With the Dil cost of Fleet Starbase construction projects driving more and more people to just buy Dil with Zen PWE is probably making significantly more than the asking price per ship any way.
I, like most people, was under the impression that if you owned the non-fleet version of a ship the fleet version was only supposed to cost 1 Ship Module instead of 4.
The fleet advanced escort seems to support this theory.
However after buying the Escort Retrofit from the vendor for 200,000 fleet credits, the Fleet Escort Retrofit still says 4 Ship Modules.
Surely this is yet another bug?
You're asking the wrong question.
The question is "did I pay Zen/C-Points for an earlier version of this particular ship?"
If the answer is "yes," then it requires one module, not four.
If the answer is "no," it requires a full four modules.
I also don't know if it applies to the ships you can pick up as slight upgrades to the T1-4 ships - for example, if you buy the Exploration Cruiser Refit (NOT the Admiral-level Exploration Cruiser Retrofit), I have no idea if you get a discount in terms of fleet modules for anything related to this ship.
If I am wrong, I would ask that someone correct this, but as I understand it, it basically turns the c-store ships into not only a ship itself (with account wide unlock), but a discount for the fleet version of that exact same ship.
The only C-Store ships that give you a discount on their fleet versions are the Nebula, Defiant Retrofit, Intrepid Retrofit, MVAE, Gal-R, and the new Assault Cruiser (I may have forgotten one). All others, even if you paid $15 for it, do not give you a discount on fleet modules. Why they didn't implement a tiered system for discounting is beyond me, although greed would be a simple enough explanation, tbh.
So in other words, if the C-Store ship you bought has a fleet version, you will only obtain a fleet module discount if the ship you bought was RA-level or higher--T5, essentially.
No idea. The Provisions cost about 20,000 Dil each for your fleet so go ahead and add that into the cost of every fleet ship when you think about them. The entire fleet system seems to be geared at making PWE money, the ships are over priced cash wise and people are paying cash for the unholy amounts of Dil required rather than grind up 8000 per day per character.