We use *options a lot to list all the possible choices in multi-select lists. I have had the experience that the returned list is trucncated. It seemed almost as if some "limit" was in force so I tried to up the limit as a workaround and low and behold, it worked.
{"type":"Topics", "sort":"name", "limit":"100"}
Yes, I think it has a default limit of something around 50. This is something of a failsafe, because without a limit, you could accidentally produce a search that yields a massive list of cards that hangs the browser, the server, or both. We could probably optimize to get around the browser issue...