Please refer to: https://en.wikipedia.org/wiki/Sample_size_determination
Specifically, you need a sample size of 100 for 90% certainty, and a sample of approximately 1000 for 97% certainty. Ultimately, how much error can we afford and what would be a reasonable sample size to determine mtDNA group 'in all probability'?
Moreover, in sampling, you need the sample out of people with the Exact Line!! Because this profile is listed as U5b - this entails a sample from her to the exact same daughters in all generations! And that assumes that all lines are correct for those people. (That means - it is unlikely to be ever found... except if you dig up 950 graves... (assuming all 50 people who are alive are contributing) i.e. the test is flawed to start with...)
Questions: Did someone gather 1000+ samples for any of the exact lines? (I think unlikely - and that is the number to hold it to a high likelyhood). Were all samples U5b? How have you allowed for 'errors'? What is the statistical strength of the test?
U5b would in my mind, today, only hold true if someone took her sample physically. On the profile there are no sources to where the test was done and how the samples were collected? If her profile is publicly attributed to be U5b, that should be surely be sourced? I recently saw a 'Barry' Y-DNA result - I think just over 100 men contributed and there were three distinct groups although they share the same progenitor. Confusing - that test must have a very low reliability :(
All users should be aware of the dangers of 'extrapolating' without emperical evidence. -the strength of the test needs to be shown otherwise or the public display of mtDNA be curbed.