I was never able to find anything in writing, suggested or reason, why or when the title Sacred Family was changed. I only read on history books that the 1514 painting on canvas, viewed and described by Vasari, on his book of 1544, became the only information, and was repeated by all the historian on Raffaello. The only information I found was that after the death of the owner Cardinal Rodolfo Pio da Carpi in 1564, it was inherited by the relatives Falco Po di Savoia Family.
This 1514 painting is acknowledged all the time, on Art History books, but there is no information of where the painting is.
While the 1518 painting on wood, known to be in the Farnese collection, is on view since 1734 in the CapodiMonte Museum in Naples, and the Sacred Family now is described as:
“The Madonna of Divine Love” by Raffaello
In searching for a reason on the change of the title of this painting, I went to the source of the description of this painting in the book
“The Lives of the Most Excellent Painters. Sculptors, and Architects by Giorgio Vasari.”
GIORGIO VASARI LIVES OF THE ARTISTS A Selection Translated by George Bull – Penguin Book
Reprinted from 1972 to 1982
The original title is “The Lives of The Most Eminent Painter’ Sculptors’ and Architects’ written by Giorgio Vasari Painter and Architect of Arezzo”