I don't know how they work from the back end perspective, I update the Galaxy-compatible content and AFAIK Galaxy should let you know on its own that you have an update :)
Grargar: If you guessed wrong, the DLCs are also unbundled and you'll have to bundle them back, before you can download a game again. I really envy the lucky folks who have all the DLCs for Sword of the Stars: The Pit. :P
Grargar: It's been a while since they have started working. We are getting no flags for galaxy-compatibility updates, because Judas doesn't flag them (at least that's what I think).
Post edited Yesterday by JudasIscariot