The key to most stuff like Ancestry.com is date and location of birth, death, marriage, and other significant dates/places. The names are almost secondary in that regard, not just because names can change by design or accident, especially if you go back more than 2-3 centuries.
This is also why if you are a criminal stopped by the police, it is important to give a false date of birth, not just a false name. It is also why Facebook and other sinister data gathering sites always want to know locations, such as where you went to school and graduated, etc etc.