Found it! Took some looking, and I couldn't find it online. Adam's book The Negative, eighth printing (1986), page 88: "The key point is at the threshold; we consider a density of 0.10 above filmbase-plus-fog density as the useful threshold. The exposure that yields this first significant net density of 0.10 is established as the Zone I exposure point.
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This procedure is applied as practical exposure information in the test that determines the film speed rating that gives 0.10 net density for Zone I exposure. If, for example, using the manufacturer's recommended ASA number, we find that a Zone I exposure produces a density higher than 0.1, we can reduce this exposure by assigning a higher ASA film speed number. If the Zone I density is consistently below 0.1 we use a lower ASA number to increase the exposure until the optimum value is achieved."
The italics in the quote above are not mine -- they are in the book. That passage is what I was remembering when I made the prior post about 0.10 above fb+f. Nice to confirm my memory isn't completely shot.
And I find that development time does indeed effect EI, just not much. When I test for EI and N development time, I have to do it iteratively. That is, I find my EI, then check for my Zone VIII density. It's usually too high, so I decrease development until I get Zone VIII where I want it. Then I retest for EI at this lesser time. I often see a decrease of around 1/3 stop in EI, so I lower the EI by that 1/3 and retest for N development time. Usually two iterations are good enough to get me very close, which is all I need.
That is part of what makes TMY-2 in XTOL 1:3 so interesting to me -- even with my decreased development time (to give me a Zone VIII of around 1.0) I still get a real film speed of around 400-500. I wasn't expecting this. I'm told that this is partly the result of continuous agitation via the Jobo. But I've never tested with other agitation methods so I can't say one way or the other.
This is just my experience. I'm not saying anyone should change anything. If something works for someone, they should by all means use it. We all do things differently, and that's a good thing. All I'm doing here is trying to add a little more data to the discussion. Because if I've learned anything in photography, it's that YMMV.
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