Though I think I've gone through all the rooms and I've even known that there is such a parchment (because I remember that the only thing that tells you that you need Expert Perception to open the doors is BEHIND the doors ).
I must have gone the right way even if I didn't know it because I used the big Baa head to get some experience and lower my reputation to get closer to Notorious. So I didn't miss anything after all.
Also thank you Ossie for explaining the Star Wars pun. Sadly I have seen only this one Star Wars movie, years ago, and in Czech localization, so I didn't recognize it (Also I'm not really a Star Wars fan.)