R-BY3374 emerged ca. 1200 AD, and from this branched a number of subclades beginning as early as 1200, 1300, 1350, 1400 AD, etc. As Big Y-700 test results for these earliest subclades almost consistently show Muir or Moore, it's clear that the progenitor of BY3374 was etymologically from a similar-sounding name (likely Mure or Mor), most probably in Ayrshire, Scotland, or in the area immediately surrounding it. There are also a number of other surnames under BY3374 which are not Mure/Muir/Moore, and they all appear to be NPEs. More to follow...