What you say makes perfect sense and fits with my experience (which is very limited). For some reason a number of folks over in the mechanics forum keep telling everybody to not trust published numbers ans measure the ERD for themselves for every rim they get.
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Bikes: 1996 Eddy Merckx Titanium EX, 1989/90 Colnago Super(issimo?) Piu(?), 1990 Concorde Aquila(hit by car while riding), others in build queue "when I get the time"