I have gone from being a moderately severe overpronator to a neutral over the course of the past couple of years. Not really sure why, but there it is. Has this happened to anyone else?
Yep, me too. I think it's because my muscle development and muscle balance are better - also I'm stretching consistently. As soon as I stop for any length of time, I can feel my body getting misaligned again, so it's a great incentive to keep going.
It happened to me too! In fact, I kept using the same shoes I was fitted for (for pronators) for years and ended up getting injured. When I got things checked out, I learned that my shoes were overcorrecting because now I was a neutral runner.
I think your form just naturally evolves over time, so it's a good idea to get fitted for shoes every few years to make sure they're still the right kind for you.