Query on Mary Ellen CLANCY

Looking at the sources attached to her profile it is obvious that multiple people have been confused

* 1930 Census - born 1882 New Foundland - married to Patrick J O'BRIEN, mother of Mary C, Anna, Joseph J, John E, William, Frank P, Elizabeth, Margaret, Robert

* 1940 Census - born 1881 Massachusetts - married to John J O'BRIEN - mother of John R, Paul I, Claire H, Robert W

* Family Search Tree - born 1891 married to John Robert O'BRIEN - mother of John

* Family Search Tree - born 1860 Massachusetts - married to John O'BRIEN - mother of George Brennon, John Henry, William, Thomas Francis, Mary E

Mary Ellen Clancy born 1881 in USA is NOT the sibling to Thomas Clancy born 1836 and the other children listed. She may have parents John Clancy and Ellen Barry BUT they are not the same John Clancy and Ellen Barry who are parents to Thomas Clancy and other children listed.
There is already one Mary Clancy in the family born 1844. From information I have she married on 18 July 1868 to John Magner.
I have a reasonable amount of info on the Clancy family (especially Thomas).

Too many people see a name and automatically assume it is a relative without checking carefully the details. Clancy is a very common name