Newcastle was a nuisance when I was recently writing an essay on the Royalists in the Civil War. In one source I used, (a letter Charles wrote to him at the start of the war) he was an Earl, the next source was after 1643 when he made a Marquess and the last source was one after the restoration when he was a Duke, so I was having to alternate between his various titles!
EDIT: It is interesting as well that many of Newcastle's lambs (the nickname was due to their white coats) also wore blue bonnets, although how quickly those wore out I do not know.