I think you have a typo for
Stacy Harris's year of death, "(1918-1873)".
I've looked into
Stacy and
Tracy before too and both seem to have been used as much for girls as boys in the 1850s in the US.
Stacy trending for girls in the 60s when all popular examples were men is probably explained by the perception that they are surnames as first names. Surname style names are perceived as unisex, so even if they are only used by one gender as first names, they can trend for the other gender if they are more common as a surname (See
Tatum). This ignores their actual origin as nicknames or archaic forms of first names.