"Amazingly, the alien's time slice has swept back through 200 years of Earth's history, and now includes events that we consider part of the distant past, like Beethoven finishing his 5th symphony."

Only if the aos is assumed to continuously have an independent existence, which it does not. Referring to fig.1 in the previous post, the aos is only determined after receiving the return signal.

CMIF simultaneity says the accelerating observer (he) MUST adopt the conclusion (about the current age of the distant person) of the perpetually-inertial observer (PIO) who is co-located and stationary with respect to him at that instant in the his life. I.e., if that PIO concludes that the distant person is currently T years old "right then", then the accelerating observer must adopt that conclusion.

SR does not mandate what the observer concludes. They are free to choose an inertial frame or a pseudo rest frame. That is the essence of the 'relativity principle'.

Also, the term 'perpetual' is redundant, it doesn't provide any useful information.

Poor choice of words. She appeared to age more slowly. Converging or diverging, the closing speed of the gap between A and B observers produces doppler shifts, perceptions that indicate changing clock rates, NOT aging.Yes. He says that the distant person got YOUNGER when he accelerated in the direction AWAY from her. That is solid CMIF.

system of synchronized clocks.

from OTEOMB, A. Einstein, 1905, par.1:

"But it is not possible without further assumption to compare, in respect of time, an event at A with an event at B. We have so far defined only an ``A time'' and a ``B time.'' We have not defined a common ``time'' for A and B, for the latter cannot be defined at all unless we establish by definition that the ``time'' required by light to travel from A to B equals the ``time'' it requires to travel from B to A.

... It is essential to have time defined by means of stationary clocks in the stationary system,"

How far can a local system be extended? Not much. The system is very hypothetical and logistically impossible. All considerations of 'time' resulted in the coordinate transformations which bridge the gap between local and distant 'time'.

If you don't understand the basics, you are just spinning your wheels.

There is no instant knowledge.