Even wuxia movies aren't in and of themselves terribly accurate when it comes to setting and costumery. There's a lot of creative liberties that are taken (in some films, less liberties are taken than more), and you'll often see elements of different time periods inserted willy nilly, missing altogether, etc.
Like Pumpkin said, the point of the game is fun. You can, of course, make every effort to be authentic - a lot of players who enjoy that type of setting will appreciate the effort (or at the very least, appreciate the atmosphere that your effort creates). But you don't need to pin down historical details for the sake of being accurate.
I tend not to care so much if there are elements of the culture thrown in gratuitously for exoticism (though I do get irritated when what's taken are [usually inaccurate] stereotypes, rather than actual cultural elements), but I do get frustrated when the players/creator think that the setting is indicative of or presents an accurate representation of the culture in question. Then yes, I do get offended - but it's not because of historical inaccuracy, but because of the arrogance.