There can still be a difference between practise and a(n insufficient) theory without there being a new theory superseding the old one. A lot of historical deve

There can still be a difference between practise and a(n insufficient) theory without there being a new theory superseding the old one. A lot of historical developments take this shape: we discover something not predicted by the theory we though would explain it, work on it for a while, and only later do we find the new theory that explains also the novel thing. For practise to be condensed into theory requires predictive power, and not all differences between practise and a theory are predictable -- yet. That said, I agree with your overall point. If one finds a difference between practise and theory, it's because one tried to use the wrong theory for the situation at hand.