Family 12 is a conflation of four different female lines, as shown by mtDNA evidence, of which two lines relate to the original Foundation Mare, arising from an error introduced in the 1891 edition of GSB assigning Whiteshirt Mare and Mother Western (grandam of Eclipse) to the same dam, making them half sisters. In fact Whiteshirt Mare was out of Lord Montague of Cowdray's Montague Mare and Mother Western was out of Montagu Mare (by Darcy's Montagu)

Dam of an unnamed mare by Hautboy through which this maternal line of the family continues, evolving into branch 12-g; all other branches of the family, 12-a to 12-f,

descend from the other Family 12 Foundation Mare, Montague Mare

The two other additional Family 12 founders arise from misattribution of two early American matrilineages to the family of imported Diana (1754, Family 12-b)