There had to be two first class carriages - one of them had to be Non-Smoking.
Ahhh yes half of coach H was smoking. First class accommodation was increased in the late 80's with seating in the restaurant/buffet carriage designated first class. The buffet cars that had standard seating were fitted out with First class and turned round in the set to join up with the other first class coaches. As we know this remained until 2014 when either half or a full coach of first removed from each HST set.
The early seating plans for the 9 car IETs showed a return to the same number of first class seats pre 2014 but that was soon changed to match what's provided currently on HSTs. There will be those who would argue whether this is a good or bad step.