AssetBundles - depend on asset already included in executable

I'm a little confused as to the operation of AssetBundles.

As I understand it, you can push and pop assetBundle dependencies, so that a texture that is required by two asset bundles is only included in one of those bundles (the parent bundle). The parent bundle then must be loaded first in order for the texture to be referenced correctly by the child assetbundle.

However, in our case, we wish to load an assetbundle that contains a new mesh (and material) to our game. Most of our textures are atlased, so the texture which this material uses is already present in the "base" version of the game (the original, built executable).

Do I still need to include this texture in the assetbundle, or does unity "know" it doesn't have to include this texture in the bundle, since it is distributed with the "base" game? Do I need to build and distribute a "parent" assetBundle containing all my "base" assets before I can do what I describe above? Or perhaps I simply need to build the parent bundle - not distribute - for the purposes of building the subsequent asset bundles; to push the dependencies for the "child" bundles? Will this allow the child bundles to reference the already-existing assets in my game?

Any clarification would be greatly appreciated! :)

Thanks