When copying movie clips from one Flash library to another, it is common to see the warning dialog "One or more library items already exist in the document" with three options:
However, "Replace existing" doesn't replace existing - it puts the duplicates into new folders. With the result that I'm trying to avoid: multiple duplicates of shared resources (e.g. bitmaps, sounds etc.) which unnecessarily bloat the end product (SWF) with duplicate resources. To fix this means a long tedious process of swapping items to eliminate the duplicates.
This is insane!
Flash CS5.5 - OS 10.7.x
While it sounds like the software might not be performing correctly for you, your swf will not be bloated by library content that is not used. Only the fla will carry the weight of unused content.
but the point is that the duplicate library content will be used unnecessarily.
It will only be used if you use it. You should set up your Publish Settings to generate a size report so that you can see what is adding weight to the swf.