I suspect the title doesn't really do justice to my question, so let me try to explain a bit more carefully. I have a couple of situations now where I'm working simultaneously on closely linked papers that refer to each other a lot. So, Paper 2 will have many citations like [Paper 1, Proposition 4.7].
Now, within one file, LaTeX deals brilliantly with referring to other parts of the same document in a way that is dynamic; if I move things so that Proposition 4.7 becomes Proposition 7.1, within the same document, things will change automatically. Is there any way to set things up so this will happen in Paper 2 when I move things in Paper 1?