Falling down a rabbit hole. Where does the SAE define a coupe by its interior passenger volume? SAE J1100 doesn't seem to have it

I fell down this rabbit hole recently because of all the automakers marketing their cars as "four door coupe" and "coupe SUV", and it made me wonder what the definitions of "coupe" or "sedan" actually are.

What I've found is that A LOT OF PEOPLE claim that the Society of Automotive Engineers defines a coupe as "a fixed roof car with no more than 33 cubic feet of interior rear passenger space," and more specifically they cite SAE J1100 as the document that provides this definition. It's so prevalent that it's made it to Wikipedia and dealership websites, and obviously in very authoritative-sounding forum posts.

The "problem" is that no version of SAE J1100 seems to contain this definition.

This version from 2001 defines motor vehicle types in Section 3.1, but it only defines passenger cars, station wagons, and hatchbacks:

3. Definitions of Terms

3.1 Motor Vehicles

3.1.1 PASSENGER CAR-A vehicle with motive power, except a multipurpose passenger vehicle, motorcycle, or trailer, designed for carrying 10 persons or less.

3.1.1.1 Station Wagon-A passenger car with an extended upper to increase the cargo and/or passenger capacity.

3.1.1.2 Нatchback-A passenger car with the rear access door encompassing the back light.

I've looked at the later versions of J1100 and this doesn't change.

Then I saw Interpretation of SAE J1100 Cargo Volume Indices brought up by Google as a search result, but I don't have access to the text and there doesn't seem to be a free one available. But this being a search result makes me think that the idea that the SAE used cargo volume to define a "coupe" is a misconception, maybe based on what they said in this document.

Soooo.....can anyone familiar with the SAE standards elucidate on where this definition came from?