I hope I'm using this forum correctly...I was a little confused by there being only one thread...
There should be a level inventory in Revit that will show a list of all levels in a drawing and in which views they can be found. The same might be helpful for grids, and maybe even other annotation types, but particularly for levels.
Sometimes, you may be in a more detailed view and not know whether a level exists or not, so you create one there and end up duplicating one that exists. This is more an issue when multiple people are working on a project. It would seriously aid in that respect, though.
Thanks!