Dr. Steve Mount is an Associate Professor of Cell Biology and Molecular Genetics at the University of Maryland. In February 2011, he wrote an article about his experience submitting his DNA to 23andMe and his experiences matching his cousins. More specifically, he became interested in one particular segment of DNA trackable to a specific ancestor.
He shares these insights.
Distant relatives (4th cousins and beyond) often share no genetic material at all.
It is possible to share a segment with very distant relatives.
Sometimes, more distant relationships are more likely.
Most of your relatives may be descended from a small fraction of your ancestors.
Genealogical time is defined as being the time span marked out by genealogical connections between individuals based on records, historical documents, archaeology, and writings about people and events at the time. If a tree can be built connecting dynasties, that tree covers genealogical time. DNA can match cousins over genealogical timeframes. DNA matching is not limited to 1st, 2nd, or 3rd cousins. Genealogical time is not limited to those close relations. But there are those who will tell you it is so limited.
From family tree dna:
https://www.familytreedna.com/learn/faq-items/genealogical-time-frame/
Genealogical Time Frame
The genealogical time frame is the most recent one to fifteen generations. Recent genealogical times are the last one to five generations.
So if a cousin and I have an MRCA 15 generations ago, we may be 30 generations apart, and be 30th cousins, for example, and only share 10 cM of FNA on one chromosome. But that connection has more confidence than if there is no shared DNA.
It is also a matter of probability.
That, BTW, is not any sort of proof - rather it is an assertion. Almost everything in geni is an assertion.
In Evidence Explained there is no mention of Genealogical time frame that I have yet found. It is not a standard of proof.
Evidence Explained does say genealogical proof is more stringent than scientific proof because one error can affects many generations and millions of people.