I've heard that Han Solo's "parsecs" line was an intentional flub by Lucas, to show that Lucas was a blowhard who didn't quite know what he was talking about. I think there's actually something about that in the script.
Fixed that for you.
No, seriously, I've heard the Solo thing before, but it never made much sense to me. Why Kenobi consider going on such an urgent mission with someone who didn't know the basics of space navigation?
Anyway, given Lucas' history of changing his story, this just sounds like another instance. But if it actually is in the script....