If you were to dig into the many old APA ,SOP you will find breeds added and removed.How these are handled with the heritage label I do not know ?At one time Cuckoo Leghorns were in the standard as Dominque Leghorns,Rose Comb Buff Leghorns were in the standard much earlier than 1981,I think they were dropped about 1923.About the same time Pile Leghorns were dropped. Some varieties have been around for many decades but never admitted Exchequer Leghorns and Mille Fluer Leghorns are two such.