Probably every franchise that's gotten beyond one or two installments (books, short stories, movies, TV series episodes) is going to have continuity problems. Star Trek is perhaps notable for being relatively free from them (at least considering the hundreds of episodes and novels involved), and for coming up with explanations to successfully retcon them away when they do happen.
Consider other franchises. Like the Humanx Commonwealth. To date, Alan Dean Foster has been the sole author in that franchise, and yet in one book, we have the insectoid Thranx taking up body-surfing, and even teaming up with a Human friend and serving as a living surfboard, and yet in a later book, ADF establishes that the Thranx, with their relatively vulnerable breathing spicules, are racially terrified of immersion in water.
Or Oz: yes, that's been a multi-author franchise since Baum died in 1919, but even during his lifetime, there were continuity glitches, with perhaps the biggest one being that in The Marvelous Land of Oz, Oz (i.e., the humbug Wizard, Oscar Zoroaster Phadrig Isaac Norman Henkle Emmannuel Ambroise Diggs) is established as having been at least tacitly complicit, and possibly one of the conspirators, in the captivity of Ozma, the rightful ruler, and yet when he returns, permanently, in Dorothy and the Wizard in Oz, he's completely forgiven, and the whole matter of his complicity in Ozma's captivity is quietly dropped. (Decades later, in the short story, "Oz and the Three Witches," Hugh Pendexter III managed to retcon away that glitch, and I think he did so quite successfully).
And personally, regarding the SW "parsec question," I'm with the EU authors on this one, assuming that the trick of the Kessel Run is to avoid the obstacle(s) in the shortest possible distance traveled.
