Even today, there is no NEC requirement that NEMA plug patterns be followed....there is only a requirement that differing systems have different patterns.
NEMA designations didn't really get codified until, I think, 1972. There were earlier attempts, as far back as 1965 (again, I think), but there were numerous changes made in the interim.
There were a number of patterns that were "rated"..that is, accepted by trade practice, and marketed for, multiple types of service. UL would list these things, and test them, as for the uses intended by the manufacturer.
Two notable exceptions to the use of NEMA patterns are Recreational Vehicles (which still have their own pattern) and the three-prong clothes dryer and range devices (which are being phased out). Indeed, the computer you posted from probably has a non-NEMA 120 plug on the back of the monitor.
NEMA stands for "National Electrical Manufacturers' Association. They would have the definite answers to your questions. UL also has published "standards" that define their listing criteria.
