With regards to mate references, online help it states you can define "Multiple mated entities". Each mate reference can contain up to three mated entities. Each of these entities can have an assigned mate type and alignment.
For example, a shaft can have its cylindrical face assigned to a concentric mate and its planar end face assigned to a coincident mate. When you drag that component into an appropriate location in an assembly, the software adds both mates.
This appears to be true when only adding a part (with mate refs) to an assy (with the same mate refs), but it DOESN'T work for adding a sub-assy (with mate refs) to an assy (with the same mate refs).
Has anyone else seen/confirmed this before?