Small nit, I worked on TypePad directly and it was very influenced by Moveable Type (and maybe some copied code) but it wasn't an instance of Moveable Type. E.g. there was never a time where you could patch TypePad with a MoveableType update. The architecture transition was primarily to stop rebuilding pages after every edit, but that also ended up being a good excuse to try to clean up a bunch of other things too.