You seemed to answer your own question, but I'll add this anyway.

a plane of simultaneity may crosscut my past therefore a different version of me experiencing my past exists in another reference frame,

yes, And that plain of simultaneity will pass through alpha centauri in four years. And what it does, the alien with a telescope we'll see you different than you will be then.

therefore there's millions of copies of me one per reference frame.

One per observer. Any number of them. And they're all you — specifically, the gravity waves and light you created are spreading out across the universe.

But that's all you are to anyone else unless you touch them, even if they're standing in the same room with you.

it doesn't mean you are somehow duplicated when you're at these contrasting coordinate in my frame.

In a sense, you are continuously being duplicated, because you broadcast your existence out to the universe through gravity waves and emitted light, and other ways you distort the universe. These distortions propagate at c.

Unless you touch somebody, these remote distortions are the only mutual existence you'll ever have with anyone.

When we meet up our coordinates roughly line up so we don't notice this.

When you're close together in the same room, then you don't notice it. That's because the speed of light is so fast. When NASA talked to the astronauts, there was a two-second delay because NASA was actually talking to someone in the past.

You seemed to answer your own question, but I'll add this anyway.

a plane of simultaneity may crosscut my past therefore a different version of me experiencing my past exists in another reference frame,

yes, and that plain of simultaneity will pass through alpha centauri in four years. And when it does, the alien with a telescope we'll see you different than you will be then. There will be two copies of you, separated by 4 light years of space and 4 years of time.

therefore there's millions of copies of me one per reference frame.

One per observer. Any number of them. And they're all you — specifically, the gravity waves and light you created are spreading out across the universe.

But that's all you are to anyone else unless you touch them, even if they're standing in the same room with you.

it doesn't mean you are somehow duplicated when you're at these contrasting coordinate in my frame.

In a sense, you are continuously being duplicated, because you broadcast your existence out to the universe through gravity waves and emitted light, and other ways you distort the universe. These distortions propagate at c.

Unless you touch somebody, these remote distortions are the only mutual existence you'll ever have with anyone.

When we meet up our coordinates roughly line up so we don't notice this.

When you're close together in the same room, then you don't notice it. That's because the speed of light is so fast. When NASA talked to the astronauts, there was a two-second delay because NASA was actually talking to someone in the past.