Today I got a copy of Heraldic Cadency: The Development of Differencing of Coats of Arms for Kinsmen and Other Purposes by Lt.-Col. Robert Gayre, published in 1956. Also arrived: The Nature of Arms: An Exposition of the Meaning and Significance of Heraldry with Special Reference to its Nobiliary Aspects also by Robert Gayre. Published in 1961. As you can see, Gayre was fond of lengthy subtitles for his works. I suppose that was part of his multi-faceted neuroses. He was bonkers but the books are lovely. Look ’em up. They can be obtained inexpensively from one of the usual suspects.