That would be interesting to find out GM's standards and their recommended break-in.I recently read an in depth article on brake pad lining composition and the bedding in process you cite is only for certain lining compositions.
There are a multitude of pad break in procedures depending on the type and composition of lining materials. Using the wrong one for the material can be very bad.
I am almost certain GM is now using the low/no copper linings now earlier than required by law.
I'll have to put in a question to a friend in Warren to see if I can get a composition to determine the correct break in procedure for our cars.