As far as claiming John Smith, Esq was fictional, or at least his affiliation with the Carrington line is, I get it. Lots of people mess up that info. It's easier for Geni to say his story is fake rather than deal with the myriad of folks who try to connect their tree to his. This is a major reason the info on SmithsWorldWide.org is so tainted. There are a lot of folks simply doing bad research (and I suspect they know it). I would also challenge anyone who cites John Horace Round to to try to prove him wrong if they wish to blindly accept his claims. If they try, they will succeed. I would like to see him removed as a source on here for the Carrington/Smith story based upon my findings. I will continue to insist that he is wrong in the Smith/Carrington matter as it pertains to the Smiths of Rivenhall specifically.
Scientists can demonstrate, clearly, that humans possess the genes of Neanderthal. I don't think proving shared DNA with two people whose TMRCA is 500-700 years would be impossible. You'll need scientific and academic precision, however. Not something AncestryDNA or FTDNA provides at the moment.
From what I've seen, the 5-7 generation limit for what is easily found by algorithms or simple searches of matches in a list. As for what can be found using the advanced tools on GEDmatch , I think 15 generations is easily achieved. Sound genealogical research techniques are also necessary to try to extend trees into the appropriate ranges to accommodate estimated TMRCAs of 600 years. This is where most automated matching systems fall short. They can match the DNA but don't know how to build papertrails to explain it. I doubt most people have any branch of their trees that goes 600 years back on paper. Some do, but I suspect it's the exception. My Smith line sat at a brick wall in 1783 for about 25 years until I picked up where my dad left off (based on recorded family history) and started my research about 14 years ago.
As far as proving out who Hamonis de Carington was, my suspicions are we will need someone in Normandy, France who can read middle age French or Latin. The Historical Society of Normandy should have the appropriate records, if they still exist after all these years. Butterworth mentions his source I believe.
Also, after doing a little bit of refining, I find that the person who descends from Jane Marler and matches on Cr15 with my cousins also shares 22.3cM on Cr1 with my cousin who has a TMRCA with me of 1783 (7 generations, same Smith line).
The right half of this very large segment on Cr1 (about 17cM) triangulates with my yDNA matched cousin whose TMRCA with my group is beyond 10 generations.
I wish I could post pictures on this thread. It'd make it easier to share what I'm seeing.
Essentially, the descendant of Jane Marler shares around 17.5cM of triangulated autosomal DNA with my cousins.
Cr1 - 88190037 to 107846098
I will admit this is only a little high for such a distant suggested relationship, so I will examine this match further.
The descendant of Jane Marler also matches my 3rd cousin 1R Smith at 6.3cM on Cr20. Lots of nice grouped matches in this info.
Endogamy can explain this situation as well. Lots of stuff that looks to be more than coincidence.