In comments here, an assertion was made that O-ren Ishii's sword that she used to fight The Bride in Kill Bill wasn't a Hattori Hanzo sword.
Is there any information either way?
It is never explained, but all details about the sword leads that it wasn't.
O-Ren Ishii last words:
O-Ren utters with her dying breath "That really was a Hattori Hanzo sword", having been close enough to both see the symbol of Hattori Hanzo and feel the blade.
By her last words and how she looked surprised, we can believe that her own sword wasn't made by Hattori Hanzo.
And taking @Walt's comment as another possibility:
In any case, as the comments there correctly assert, there's no emblem on it, and even if it was a Hanzo sword, it was certainly not made for her because she's way too young. She's about 29 in this movie and Hanzo stopped making swords 28 years ago, when she was 1.
A little bit more information about the sword and when O-Ren used it:
O-Ren's sword was only seen being used twice. First time was during the Yakuza bosses council meeting where O-Ren is seen decapitating Boss Tanaka for bring up her Chinese and American heritage as a negative. The second and last time, is when she and Beatrix Kiddo fight with both of their swords. The lack of a hand guard (tsuba) or handle wrapping classifies this sword as aikuchi (匕首?) (literally "fitting mouth"). Aikuchi is a form of mounting for small Japanese swords in which the handle and the scabbard meet without a guard (tsuba) in between. Aikuchi is style of sword mounting that is popular with Japanese nobility, perhaphs signifying O-Ren's status as Queen of the undeworld in Japan. Her particular sword is notable due to the sakura (cherry blossom) design on the handle (tsuka).
No, it wasn't. O-ren's sword was the same that the young o-ren killed the man who killed her father with.
Her sword wasn't made from Hattori Hanzo because Uma Thurman's sword broke it in half.