I think the meaning of my OP wasn’t clear. I understand about relative frames of reference. But I’m the experiment I referenced in the OP, two clocks were separated and brought back together. Outside frames of regency shouldn’t come into play.
I think Whack-a-Mole understands the gist of it:
Einstein was famous for his gedankenexperiments - accelerating elevators and blind beetles - so let me propose one. You are standing on the sun with 3 clocks all set to the same time. You reach out with your very long arms and set one on Mercury and one one Pluto simultaneously and let them go along their way.
After a year, you reach out and pluck them off of their respective planets, put all three together again and check their times against your control clock. If Whack’s speeds are right, the Pluto clock will be slower and Mercury’s slower still, right?
So their individual speeds do matter in a real way to the clocks - not just a frame of reference way.
Ok, now, suppose you have 3 clocks all set to the same time. From your spot on the sun, you reach out and place one on the earth and one one a rocket sitting on earth. The earth is traveling at 66,000 mph in its orbit around you. As soon as you place the clock on the rocket, it blasts off the earth with 66,000 mph’s worth of thrust in the opposite direction of earths orbit. Essentially causing it to become stationary from your sun frame of reference. 365 days later, the earth catches up to it bringing those 2 clocks together. You reach out and bring them to the sun and compare their times. What will be relative times of the clocks? Will the rocket clock’s time be slower or faster than the earth clock?