Hi Mags,
thanks for your question/post.
Can I suggest that you edit it and specifically mention that you've got your mtDNA test results back? It might confuse other people (it did confuse me in the beginning) as your title is too general (I was assuming you mean an atDNA test as that's what the majority of people takes).
Some comments, thoughts from my side, please correct me if I'm wrong as I'm not an expert on mtDNA.
It seems to me that your haplogroup is very high up the phylotree (same as my mtDNA haplogroup, see my discussion lately on it's respective category). That means I assume your common ancestor (the lady who is the originating mother of that haplogroup) is most likely a couple thousand years ago.
You also mention that 5% of haplogroup H is in the H1b1-T16362c haplogroup. So some quick calculations on the edge of a napkin. Haplogroup H is considered 40% of all mothers in Europe (see https://en.wikipedia.org/wiki/Haplogroup_H_(mtDNA)). Europe currently has a population of 742.5 million people (as of 2013). That means there are a minimum of 297 million people with Haplogroup H in Europe alone, I guess we can easily add another 300 million for the rest of the world but let's keep it at 300 million for easier calculation.
5% of that 300 million is 15 million. So you have roughly 15 million if not a lot more people that match you on your mtDNA haplogroup H1b1-T16362c.
It's safe to assume that those with 0 difference are more recent than the couple thousand years (as they also match you in more detailed markers downstream which might not be identified yet as being ancestral).
Still, I don't believe it makes sense to compare family trees and find a needle in a haystack.
For sure those with a difference > 0 don't make any sense. I quote Ian Logan again who's a way more well known expert on mtDNA than anyone else I know:
"I usually suggest an average of 400 years for a HVI1 & HVR2 mutation (also 521-4, 573.1C, 16183-16193) and 1,600 years for a coding region mutation.
So certainly a perfect match can be with all maternal relations in the last 500 years (consider King Richard III and his perfect matches at 'J1c2c3'), or not even match perfectly with one's own mother !"
Also, different than Y-DNA the mutations of mtDNA are much harder to estimate. Sometimes you have none for many generations and I think I read somewhere that someone had 3 (?) in one generation. In general 1 mutation happens every 16 generations (if I interpret Ian's quote correctly) assuming 25 years per generation (400 / 25 = 16).
So in the case you mentioned I assume that you have a paper trail to that common ancestor and both of your have the same mtDNA, right? Only in those cases you can be sure to mark them as proven by DNA.
If you do the reverse (finding a common ancestor with someone who has 0 difference) might be a tough game as you can basically search for 400 years and still might not find a common ancestor (as 400 years is just the average).
I have come to the conclusion that mtDNA test is basically worthless for any conclusion in the genealogical time frame, I rather use atDNA and find a match there through triangulation. Some of my matches must be following the all maternal line (for 5 generations it's 1 of 32, for 6 generations 1 of 64 matches).
But these are just my personal opinion.
