Maybe I misundertand something, but I find Greg Egan's treatment of the simultaneity problem between distant clones in Diaspora problematic, strangely at odds with the overall technically detailed rigorous style of the book. Consider this in Chapter 11:
Elena had chose not to wake if any other versions of her had already encountered life. Whatever fate befell each of the remaining ships, every other version of him would have to live without her.
But this is surely unattainable, given the clones are tens of light years dispersed into different directions! Let's say clone #1 just encountered life, and clone #2 seventy light years away is about to encounter life very soon. There's no way to prevent #2 from waking because by the time message of encountering life from #1 arrived 70 years later, it would be too late.
Special relativity 101 tells us in cases like these, there will be some frame of reference from whose perspective #1 encounter life first, and another frame of reference from whose perspective #2 encounter life first. There's no objective claim to which clone encountered life first, and both clones will end up waking! Given fragmentation of identity is a major theme and pathos of the story, I find it unlikely that GE is just sweeping this basic limitation under the rug for (in)convenience.
I hope I'm not being too serious, because this is a wonderfully super-technical serious story ;-P