Trying to mirror an assembly with assembly features in it to an opposite hand assembly

1, mirror assembly

Took 2 parts, made an assembly added assembly feature holes on LHS. Insert mirrored parts, Holes lost.

2, mirror assembly

Made an assembly from the assembly above

Choosing just to mirror without opposite hand just makes a copy of the original ?

Assembly features holes ,are not carried in to the mirrored assembly when opposite hand version required.

(is that not what a mirrored assembly is?)

Any ideas on how to copy an assembly with holes drilled in the assemblied stage, to a OH assembly?

Thanks