OK I am back from the books.
Before the 1928 NEC added rule 613 demand factor tables, there were no prescriptive methods for 'diversity' sizing what we now call services and feeders.
There were rules on sizing branch circuits but not feeders. And there were no 'demand factors'.
However nothing would have prevented a PE from sizing a feeder smaller than the connected load as long as the feeder conductors were properly protected.
The NEC did require a feeder be replaced if the load was found to be too great.
The 1929 supplement added the definition 'demand factor' to the NEC.
1930 NEC rule 808(k): said:
In many cases conductors of a feeder or main circuit supplying a group of motors need not have a carrying capacity equal to the sum of the full load current ratings of the motors supplied. A diversity factor may be permitted by the authority having jurisdiction of these regulations to be used in determining the carrying capacity of these feeders or main circuits, the value of this factor depending on the size and number of the motors supplied and the character of the load.
Although the idea only applied to motors.
1933 NEC 405d: said:
Service Switch rating
The service switch shall, unless a demand factor has been granted, have a rating sufficient to carry the total connected load, and have a rating not less than the rating of the cutout base or the setting of the circuit breaker in series with it.
In 1937 the code is rearranged and article 220 is born:
1937 Report of Electrical committee said:
Article 220--Feeders.
In contrast with the direction of the rules adopted for Article 210 as to
adequacy of wiring layouts is the further recognition extended in this article
to the diversity of use of appliances, other than motors and the resulting
appropriate economies in the amount of copper permanently installed as
feeder conductors.
It is appropriate to make special mention of the extensive
authoritative data covering the ratio of "demand" or use to current rating of
connected load secured and presented by the Electric Light and Power Group.
Consideration of this data resulted after full discussion in material decreases
in the demand factors specified for installations of domestic electric ranges
rated at 3.5 kilowatts or larger
By 1940 the code is first requiring the loads to be computed:
1940 NEC said:
The conductors of feeders shall not be smaller than as specified in Tables 1 and 2, chap 37, for the computed load feeder loads.
So between 1928 and 1940 engineers and electrician designers had some wiggle room with the AHJ. Before 1928 code did not address it.