A history of sauces
First before anything else, we should recognize that if it weren't for the battalion of Italian cooks that Catherine De Medici took with her to France when she married the Duke of Orleans (...later to become King Henry II in 1553...), then the French would still be tearing at their food with crude tools. Later in the seventeenth century, cats like Varenne, Careme, and Escoffier developed the "sauce system". Careme had only four (espagnole, veloute, bechemel, and allemande). Escoffier had five which included the first three originals, but excluded allemande and added tomato and hollandaise. That being said, there should never be a debate in regards to what the original mother sauces are. However, there a butt load of derivatives that are open to debate and discussion...beurre blanc being a hot little topic itself. Also, what is a true demi-glace and how a demi is very different from an espagnole. Thickening agents, when to use and when not to use opting for a true reduction instead. So, all in all, we can't go back in time and change/add to the original mother sauces. It's like the Bible, man. It's already been written and you can't add anything to it, but you can sure have a h*ll of alot of fun with your personal interpretation of it. As for the source of my comments, I'm huge fan of "The Sauce Bible" by David Paul Larousse.