You are on the right track with your thinking. Here is from my experience on how vesys works.
It only checks the database on parts when you first open Vesys.
If you add a NEW part through the component manager it will not show up as a selectable in vesys until you do a refresh all
Often parts in my database might not have a symbol , so I update the symbol, then do a refresh all, then reselect symbol.
It will also take care of supplier and costomer part numbers on the face of the drawing.
Batch update library parts is typically done for parts that you have already incorporated into a harness and you updated the guts of the component.
If I make changes to how a part works like terminals and deeper type technical information that information will not come through on a harness until you force it with the batch update application. The annoying thing is that you have to do this in every harness in which that now updated part is used.
It makes it very critical that you setup your parts in your library correctly.
In short.. New part not in drawing, Refresh all.. then you can use.
Existing part and you made changes to how it works, Batch update parts.