Duologies? Quadrologies? Are those even words?

[MDavis]

Are publishers inclined to shy away from multi book projects that aren't trilogies? I've finished my first novel and am halfway through the second, but I only imagine them as two complementing, stand-alone stories. I also have an idea for another pair of stories set about a hundred years later.

Does anyone know of any series marketed as "duologies" or "quadrologies?" I can only think of the Oathbound series by Mercedes Lackey, and Valdemar was already an established series when she wrote those.

Thanks!