User blog comment:Xilinoc/Ch. 676 - Horn of Salvation/@comment-28643013-20160603205143/@comment-25251896-20160603210718

Kubo-sensei explained it off as he never used his shinigami powers, so it can't be considered a true "bankai" or "shikai". He was apparently using his Quincy side until he was in mortal danger when his shinigami/hollow side took over (because old man Zangetsu was the source of his power most of the time, and we now know the old man represents Ichigo's Quincy power).

When it was time to reforge his zanpakutou, he got his butt handed to him by all the asauchi because he was never/hardly used his shinigami powers, always relying on his Quincy powers, which led to that whole flashback between Isshin and the Ishida clan. By learning of his lineage, he can finally realizes the essence of his power. I think the "reforging" was really just finally bringing out his true zanpakutou. If that made any sense.