Board Thread:Questions and Answers/@comment-10797017-20130622101437/@comment-44061-20140606010350

Oetsu didn't reforge a bankai he had to reforge the entire sword. This is why ichigo had to go through that whole situation of finding out his heritage and coming to terms with that. Hence why Oetsu says in Chapter 539 for Ichigo to say goodbye to his current zanpakuto, Zangetsu (not Tensa Zangetsu). In the following chapters 540-541 clearly Ichigo is not in bankai. If a new one has to be reforged then it means he has to start from scratch. Hence the whole Asauchi training situation. Ichigo has yet to enter bankai, nobody came back from the Royal Palace in bankai mode.