For the last wheels that I built, I accidentally measured from the end of the bend instead of the middle of the bend. This made me order 1mm longer sapim spokes. Then, the spokes I received had up to 1.5mm of differences in length. And the holes on the flange can be a little off center, I'd say 0.5mm.
So the result was most spoke tips ending 1mm above the nipple slot, but a few were at the top of the nipple head. Sapim 12 and 14mm nipples can have the spoke tips bottom out when they are around 0.5mm above the nipple head. But there were 2 spokes that went a further 1mm, so the tip was 1.5mm to 2mm above the spoke head. I simply turn the spoke 2 or 3 revolutions further after bottoming out. I don't think it's a problem and may help with retention.