Concerning Spot: "He" was mentioned to be more than 15 years old by now.
I am surprised. Over the course of the series several actors of different varieties portrayed Spot, who was sometimes depicted as male and female (e.g. when she got kittens). The simplest solution to me was that Data had several cats over time, whom he all called "Spot".
Maybe the one Spot had several sex-changing surgeries?
Well, we know Spot was a he in some episodes but female enough to have kittens in season 6