I appreciate the information.
Thread engagement is indeed way more than adequate, but I have read of nipples popping at the base of the head.
This can be attributed to the spoke not threading all the way up into the head, causing a stress point at that location,
especially if that is the point where the nipple contacts the rim. That would not be affected by nipple length.
As these wheels are intended for a loaded touring bike, and I am a big guy, I want to alleviate that possibility.
But, now I need to understand how to measure ERD for future reference. This go round I can just add 2 or 3mm to the spoke lengths.
I guess I need to assemble the rear wheel using the spokes I have just to verify. I'll put compound on then anyway, just in case ;-)