Sometimes the mapper updates all the difficulties besides the one that you currently selected. If you sort by artist, you can easily see that. However if you sort by difficulty like me, odds are you won't see that. Even more annoying, say the mapper added a difficulty. That won't show as an update notifications. I doubt most people would check the beatmap page to find out there is a new difficulty added. I suggest adding "update available" to the beatmapset. For multiplayer it can be optional since you just want to get on with the play and not spend time downloading that difficulty that is not even up.
Possibly even include an extra thread which quickly checks for any beatmaps that may have updates while the player is at the song select or main menu. Then "Update Available" section can be added in the Ranked Status grouping in addition to already existing "Ranked", "Pending", and "Not Submitted". Of coarse then, include an "Update all beatmaps" option in the options menu for those who are not afraid that some modded stuff they did to some beatmap(s) would be overwritten.
Possibly even include an extra thread which quickly checks for any beatmaps that may have updates while the player is at the song select or main menu. Then "Update Available" section can be added in the Ranked Status grouping in addition to already existing "Ranked", "Pending", and "Not Submitted". Of coarse then, include an "Update all beatmaps" option in the options menu for those who are not afraid that some modded stuff they did to some beatmap(s) would be overwritten.