Dormant, Abeyant, Forfeited, and Extinct Peerages @ p. 395, Nevill, Earls of Salisbury, Earl of Warwick
The cited information was published by Burke's Peerage, Ltd., London, England, 1883, held in
{R500171277} (Ref: p. 395, Nevill, Earls of Salisbury, Earl of Warwick) The author/originator was Sir Bernard Burke.