Around the middle of the movie,when Brenda does the metalergical analsis on the metal fragments she found at madison square garden, She states that the metal of the sword was folded over 200 times. This is incorrect. The japanese never folded a blade more than 15-16 times, 16 folds creates 2 to the 16th power layers of steel in the blade. This is more than 65,000 layers. Folding it any more than this creates a blade with a homogenes effect, which is what you started with in the first place, before it was folded at all. This is why they did not go any further than 16 folds because it is counter productive.