Update I got an answered from mizuno
(Mizuno USA [Consumer Support])
Aug 8, 2023, 12:18 PM EDT
Good afternoon,
Thanks for contacting Mizuno USA. The two shafts that you are seeing are correct for the 6 and 7 iron. We are able to order extended shafts to ensure that we fulfill all custom length requests. These extended length shafts do not impact stepping and shaft performance in any way as the length is added in the butt section. The shafts that Nippon mentioned to you are their standard lengths and not the same as we are able to order as an OEM. Hope this helps!
( The picture 6 iron compare with a new uncut 38.5 tapered shaft)