Generally any main track authorization has to be duplicated so that at the very minumum the engineer and conductor have copies. All other crew members had to know and understand the authority and the limits. And train orders often contained main track authority in them.Yeah 1987-88 sounds about right for starting form D's for me. The train orders were actually in triplicate, the engineer getting the yellow copy. Hard to remember.
So far the best theories I've seen in this thread is the broken knuckle to explain the lingo in post 1.