Most people are lucky if they can trace their families back more than five or six generations. Tom Jaeger needed to search forwards in time and find the descendants of eight people who lived in the 7th century.
To be traceable and appear in the historical record, their relatives would need to have been wealthy, in positions of power, to have held an office of state or in the Church or to have won a battle. That’s difficult to do, generation after generation. It might be easier if they still lived in the same area as their ancestors.
But between the 7th and 11th centuries Britain was invaded by the Jutes, the Angles, the Saxons, the Vikings several times and finally by the Normans.
Every time this happened, people with wealth or in positions of power were wiped out. There were exceptions, particularly around the edges of Britain, in Scotland, Cumbria, Wales and Cornwall.