Believe most of the CN fleet was Pullman Standard, built in the early 1950s so by 1976 they were pretty tired and worn out. No doubt this is the reason Amtrak's initial fleet contained so many Budd-built cars from SP and Santa Fe. In the case of the SP's P-S fleet, those cars had undergone a significant rebuilding in the late 1950s and early 1960s, so Amtrak was able to squeeze a few more years out of them.