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@arup
I've measured the 610mm ERD for Open Sports myself and it's the value that I use for my own calculations and builds. Works fine and I get decent thread contact when I reach the final tension. But rims can vary between factory runs.
Once I had to do a rim swap with a set of wheels that had A319 rims. The new rims were supplied and at first I thought it would be a no brainer. Purely for academic (nerdy wheelbuilder) reasons I measured the ERD of the new rims and there was 1-2mm difference all the way round. The previous wheel builder had gone long on the spoke length i.e. had rounded up rather than down so there was a lot of thread poking through. No spoke cutting tool so had to get new spokes.
Therefore, if possible always measure. Don't rely on manufacturer specs or even your previously measured values. You can get away with a couple of mm with hubs specs but rim ERD values can vary even for the same model of rim. A couple of old spokes and a tape measure is all you need.