They all fit as you describe turbo, snapping in when aligned right and can be rotated around the groove with some force/resistance except 3rd gear. Clearly because it's all sorts of deformed/stretched.
It's snug, if it's not aligned right with the groove it wont slide in, kind of a "just right" fit without interference. Really, I think third's circlip popped out from just being beaten to death.
I wish I knew if the output shaft had been replaced in 2015 and then at Carpenter's in 2017. Alas, I don't know if this is the same as original shaft or not, meaning, I don't really know the service history of this shaft in particular.