There are no boundaries between components.
Each of the individual “hole” components (which have been array copied to make the overall assembly) has the hidden edges of the square faces which, when exploded, don’t disappear, but can interfere with 3d printing in some workflows. These are the “boundaries” to which I referred. For the most predictable 3d printing, the ones that don’t form the edges of the overall assembly should probably be removed to make the top face of the overall assembly a single face - same with the bottom face.
Actually, when exploded those edges are treated just like other edges, being planar they are ignored.