Kubo two years ago: "Guys guys, I have to tell you a secret... Actually, Ichigo's sword... isn't his real sword! Yeah, you see, Zangetsu is just a fake sword created by the Quincy's boss who looks just like old man Zangetsu! Why this new villain looks just like a character invented 10 years ago? Because... uhhh... well, I planned it all from the beginning, yeah!"
Kubo now:"Guys guys, I have to tell you a secret... Actually, Ichigo's sword... isn't his real sword! Yeah, turns out he had the old version of Zangetsu inside his new shitty sword that breaks too many times all along, and that's the real form of his zanpakuto, yes.
Huh, I'm just retconning shit because I don't know how to end this manga properly? Ha ha ha, how could you possibly think something like that..." *sweats profusely*