I still need some time to chew on this as I am now finally in discussions with the meter manufacturer about this business.
In the meantime, I found a couple more excellent articles about the subject...
http://www.imeko2009.it.pt/Papers/FP_603.pdf
This one gets pretty complicated at points but the highlights for me included the reference to how a voltage sag is typically 'characterized' (paragraph 2.1) in IEC EN 61000-4-30 in terms of duration below a threshold and the lowest rms ('residual voltage') measured in that time.
In paragraph 5.1 they echo what you had said about measurements for the event starting at the zero-crossing, and the measurement of rms on a one cycle basis in 1/2 cycle increments is what my meter does.
http://www.dranetz-bmi.com/pdf/toolbox.pdf
This article is very interesting in its discussion of the variation of power quality susceptibility for various equipment. I think the backstory to this article may relate to how generalized the ITIC curve is and how it may not be useful for evaluation of whether or not the points plotted on it are 'realistic' in terms of possible impact. Maybe someday pq instruments will use IEEE 1346 for plotting disturbance events (maybe some do already?)...considering that article was written in 2000 it might be about time
