There are a lot of ways to be mistaken that you're sweeping under the rug. For example, the geocentric model worked reasonably well for predicting the movements of planets.

The scientific revolutions that Kuhn was talking about often don't make the old model entirely invalid, but rather an approximation that works reasonable well in a limited domain. So the old model is not entirely true, but it's sorta true. If you're the sort of person who wants to say that theories are either true or false, it's an edge case that's not easily handled.