>>In that case then the furthest west point of the contrail would be the last part to fall into shadow.<<
It is not falling into shadow. It is being blocked by thin haze, and quite a few miles of it, since it is so close to the horizon.
I was just in Hawaii and watched the sun do the exact same thing, regarding the haze. But since it is the sun, nobody interprets its reduction in light as “falling into shadow”.
People are looking at these videos with only one paradigm in mind. Try looking at the pictures and video and intentionally assume it is a rocket, and then try the same thing but intentionally assume it is an airplane. It should become pretty obvious to you which it is at that point. It did for me.
I have looked at every video and still pic anyone has linked to and then some. The more I see the more certain I am that it was a very big missile with a solid rocket motor. The contrail clearly passes in front of what you call haze.