I don't think any new Generation Ships have been found/added since I last updated my megathread about them, a few years ago.
I posted some musings on Generation Ships in a thread in the main forum, and popular demand (well, OK, it was DNA-Decay, but I'm sure he's quite popular in some parts) requested I post the information in the Lore subforum, so it didn't get lost. Rather than simply duplicate it, I'll reformat it...
forums.frontier.co.uk
But to answer your questions:
How many? Sixteen, though I believe the Golconda has now been removed from the game.
Are there more out there? In-game logically, yes, there are bound to be several dozen more of them. But from a meta-game perspective, probably not. Someone had to design and write the backstories of each megaship. It would be a waste of time and resources to design a game feature that literally no-one ever saw. So I think if FD put a generation ship in some far-off system no-one's ever visited yet and is unlikely to visit any time this century, they'd have put out some breadcrumbs helping people find it. I believe all of the current fleet of generation ships had satellite breadcrumbs pointing to them, and there aren't any known satellites for which the final destination is still unknown.
Now that generation ships instantly popup as anomalies in the system scanner, they're much easier to find too. SO I think we can safely assume all the ships already put into the game have been found.
Will they add more? Maybe, if the story demands it, but "doing the generation ship" thing was already done with the Golconda events; I doubt they'd want to repeat themselves so obviously.
