@SillyGoose most courses I had didn't even really use one specific book - they usually said something like "we're mostly following X, but here's a bunch of other resources that are also relevant"
yes, in the best case they had their own notes. When they do follow a book closely, it's because their notes have been published as a book. Of all the courses I took, I think a couple followed (a subset of) a book closely and the author was not the lecturer/previous lecturer at the same uni
some lecture notes i have received so far (not many years to be fair) have seemed incomplete--so i end up just working through a book on the subject xD. would like to experience exceptional lecture notes one day