For a couple years, I have been assisting my co-worker Ron work on his New York roots. We determined that his great grandfather, Harry R. Davidson, was born about 1866 in New York City, and that Harry's father was John Davidson, a native of Scotland.
John Davidson is found in the 1870 Census with a wife named Hannah, and two sons, Henry, born about 1865 or 1866, and Frank, born about 1868. Moving ahead to the 1880 U.S. Census, we find John Davidson with sons Henry and Frank, ages 14 and 11. In this particular census year, his wife is listed as Johanna, and there are two other children, Caroline age 4, and Martha, age 2. This caused us to consider the possibility that between 1870 and 1880, John Davidson's first wife died, and that he re-married, and had two more children.
A marriage record at FamilySearch.org, retrieved a marriage record that listed John Davidson marrying a Johanna Boole in Manhattan on March 25, 1875.
This leads us to the marriage record of Harry R. Davidson and Mary Crinnion.
They were married in the state of New York on December 7, 1883. If you look closely at the words next to the line mother's maiden name, it says that Harry's mother died years ago, but his stepmother was named Johanna Boole!
This leads Ron to a whole new line of members of the Davidson family that share his DNA! Hopefully the cousins can connect, and each line will have a more complete family tree. If you have the patience to wait for it, it may be very beneficial to you to order the original vital record for your ancestors, if possible.