If you open say V4 in the Assembly room and lock,  Convert V4  to a Vertex in the Model room and work on.
Open say a cylinder (vertex), in the Model room ,and work on in the Model room .( using the V4 as the dimension/scaling  base.)

If you go back to the Assembly room you will find V4 and the Cylinder are locked together.

I think maybe that this is the intent of that tute?

bwtr