I've always hated published ERD measurements, and would greatly prefer rims to publish the actual measurement of the diameter at the spoke nipple seat.
I believe ERD fails as a standard because it includes an assumption about the desired height of the spoke in the nipple. You measured to the top of the nipple, and called that the ERD. The rim maker probably assumed the builder would want the spoke ending short of the top, possibly at the height of the screw slot and called that the ERD. The difference of 1mm on each end means a difference of 2mm in ERD. A different assumption about the desired spoke height would likewise mean different ERD.
This is the core of my objection to published ERD. It's like playing the Newlywed game, where the wheel builder has to guess what the rim maker thinks about his desired spoke height.
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