I'd advise clarity even if a reader will feel patronized--it's better to say too much than not enough, if you have scope to spare. I've been listening to a lot of audio courses which drive the point home, because I am learning a lot, and so yes perhaps I already know something of what's being told, but somebody else will not, so it's still valuable to put in there. (Though then sometimes I want to stand up and shout at the professor to say that the frame story of Sir Gawain and the Green Knight is the same as the Irish myth of Cú Roí and Cú Chulainn, because why wouldn't she mention that when talking about Gawain, but that's my problem!)