Substantial proportions in the Appalachians and wherever there was significant Appalachian diaspora later will also have Welsh ancestry: now there's your ultimate forgotten ancestral grouping, later migration to Scranton, PA and some Mormons notwithstanding.
I have significant Welsh ancestry. In fact I'm almost 100% British according to my test results, mix of English, Scottish, and Welsh. (They have updated the results a few times to show Irish or various Scandinavian is also mixed in there a tiny amount, I'm guessing because Vikings in the latter case, but the other three are much larger and constant in every update.) But I didn't even know about the Welsh part prior to taking the DNA test.
I'd be a little careful with those as actual measures;
among other things they measure your DNA and not your heritage, so that means you might randomly end up with more or less DNA from different branches. I have two friends who are brothers, both half-Ecuadorian and half white American, and they ended up with pretty different ancestry DNA test results -- one had much more African and European ancestry and one had much more Native American ancestry.
My theory is that one is far more likely for people to tag their English ancestry if it was via New England as opposed to the South.
Stated 'English' ancestry in the US census has for a long time mostly indicated known ancestry from New England, which is why the patterns are interesting even if they don't show what they purport to.
In fairness in the south it's usually been an indicator of "I'm affluent." (thus usually also corresponding to the pattern Torie talked about as far as who has access to genealogy.)
