I'm betting poorer Clans without shipyards spent the centuries stripping parts from parked warships to keep there fleets operational. Lot easier to pull turrets from a parked ship then to bargain depot time from another Clan.
Not really . . . its how the Ravens survived, they rented out their expertise. Viper fluff talks about how they had a harder time with their fleet than nearly any other Clan due to Raven animosity, I think it gets hinted at in the Mercer DS fluff along with other places.
As Kit pointed out the caches, probably 6- one for each Pentagon world where the SLDF put ships and one for Strana Mechty where Nik put ships from his mini-exodus- were Clan wide property and MAYBE some of the stronger Clans had their own, which would be where things like Widowmaker/Mongoose/Burrock salvaged ships went (Wolf/Jag/Adder), merchant-powerful Clans put temporarily unneeded JS or transport CC ships (Sharks & Cats), or Clans that built their own warships parked them after mothballing their under performers (Wolf/Falcon/one other?). IIRC the Conqueror fluff talks about how the project was started in the 3040s and then put on hold when the Ravens figured out they would have no part in the Invasion, it was restarted later in the 50s.
We have never found out what it takes to pull a ship out of the communal pool . . . which is interesting since we have (and will) never be given a exact run down what is in the caches though we know a few things (like a few more Kimagures were present). We CAN say that whatever was present, there were no more really useable Yorks since the Clans built quite a few new ones after refitting all the viable hulls. We can also say that whatever else is present, the Fredasa does a better job or was easier/better for some reason that anything that remained because the Fredasa was designed & built and put into production to spread among the Clans. Whatever JS are still in the caches, building the new Hunter/Odyssey/Comitatus was deemed a better choice for the Clans that designed & produced them (GB/?/SR).
So does getting a ship out have to pass a Grand Council vote? Which would ultimately lead to a Trial of Refusal involved the party that wants a specific warship against the Clans that do not want the ship given out? Fight a Trial of Possession against the Elementals of the Ebon Keshik? Wander out and take the ship?