Theory and measurement don’t agree. Which is right?

There are errors in the logic leading to erroneous assumptions.

First: why would you measure "small" parameters if you are designing for "Q" at something better than 85 or 90dB SPL output in your finished enclosure..

I measure raw speaker parameters at 2.83 volts input.
 
Papers are not standards.
They call it a standard, that was my typo.

Although if nobody is enforced to comply with it and there are also zero consequences if you don't..........
You end up in chicken-egg discussions with these manufactures.
(I have had my fair share)

At the end of the day consumers as well as system integrators/developers have to either just hope, guess or rely on 3rd party measurements.

Kinda sad anno 2023 (almost 2024).
 
Relevant measurement levels is context dependent. If I wish to design a near field monitor for my computer setup or if the setup is for a PA system for a large arena the expected power input to the loudspeaker drivers will be two or three orders of magnitude appart.