I thought the "Q" tradition was supposed to be things common to Matthew and Luke but not Mark, as Mark is viewed as a source for both Matthew and Luke but there are additional items in both that do not appear in Mark.
You are right
I've read the Q test supposedly containst those passages that a common to all three synoptic Gospels and there is supposedly yet another text which contains the passages which are common only to Matthew and Luke. Again, if these other texts existed I would expected to see them mentioned and quoted by the earliest Church fathers.