Old shikai as in ss arc shikai. Since omz isn't zangetsu, the sword at that point wasn't actually zangetsu. True zangetsu was only revealed when it was reforged properly. That's what I meant. It was a pseudo zangetsu as simply put, it wasn't fully zangetsu - only a fraction of it (and its power according to omz), making it pseudo.

It's never stated that only the spirit particles of the hollow powers and the Quincy powers were taken. As far as I'm aware there's no evidence for it either. It's implied when YH is stealing the powers that Ichigo is also losing the spirits as well (he says something along the lines of "it's fading, the Quincy power from my mother and my shinigami powers from my father" with panels of omz and zangetsu. Implying that they're taken too. If that is the case then it still makes no sense that Ichigo's bankai blade doesn't reform into something else as at least one key component (zangetsu spirit) is missing for the bankai sword to be the way it is. I get that he was still in bankai but that's not what I meant.