The documentary has forensic anthropologists examining the bones and going back into his birth history. The bones support the assertion and the birth notes mention some physical differences at birth.
Sounds about as convincing as is possible given the time elapsed.
Also, just to say: they apparently only tested mitochondrial DNA, which is not conclusive, especially if you’re talking about northern European heritage. If there is any current known descendant and they tested the autosomal DNA, that would be more conclusive, since there wouldn’t have been any other family members that we know of in the area to be buried in that spot at that time.
Harper Steele and Will Ferrell’s road trip and documentary, Will & Harper, profiled here:
It looks like I’m unoriginal in my name selection. I didn’t keep the same first letter of my deadname though.
I guess I’m original, but I did keep my initials the same. I ended up with a stupidly long name, though. Between my first, middle, and last names, my name totals 24 characters.
My full (to be) legal name is 30 characters… 
And I didn’t keep any initials but the last name.
I kept the same initials. Other than that, I changed everything, but in such a way that I kept my scrawled signature, so I’m still TJ B-squiggle-loop.
I kept the family name. My surname is Spanish & my birth name was Irish- so I kept that setup - Kathleen.
And I took my mother’s name as my middle name; Rita.
I came up with my first name by feminizing the name my mother was originally going to name me. I was originally supposed to be Daniel Alan, but there used to be some character from a song or a poem or something named Dangerous Dan McGrew, and my parents inexplicably thought kids of my generation would be familiar with that and make fun of me. So they went with a different D name, and then on the way to the hospital realized my initials were going to be DAM, so that wouldn’t do, so they gave me the wonderful middle name of Earl instead. Anyway, so I went with Danielle, and then searched the family tree for female E names and noticed a whole bunch of Elizabeths.
Someday, I would love to be able to relate how Morgan decided on her name. I don’t know, and to hear her tell it, she does not know (or care to relate) how she came to decide. It is nothing like her birth name. But she took my last name as her middle name, so, I mean, what’s not to love?
It could just be a name she liked. I initially tried on the name Michelle, just because I liked the name, but it never felt like me. When I landed on Danielle, and Dani for short, it just fit me so well that I started introducing myself to new people as Dani (they probably assumed Danny) even before I transitioned.
That is shockingly accurate.
