I've NEVER had a male fitting screw ALL the way into a female fitting EVER.
Most of the way in is fine.....
You can GENTLY take a triangular file into the grooves of the male fitting and deepen the grooves and it will screw in further. If you were patient and knew what you were doing, you could make it screw all the way in like this.
Don't think it's necessary though. If all fittings are Schedule 40, it's cool.