On top of that even if they were able to sequence things perfectly the thing they are actually measuring is a very fuzzy thing. Like it's no surprise that one

On top of that even if they were able to sequence things perfectly the thing they are actually measuring is a very fuzzy thing. Like it's no surprise that one of the test had one twin from England but the other from Scotland/Ireland because people having been moving between those 3 countries for millennia so there isn't really a platonic idea of 'English DNA' it's just markers that tend to show up in England, but also show up near England but somewhat less and may also randomly popup other places, but usually not all of them in one other place.