Aside: Ever seen Back to the Future 2? In it, the main character, Marty (played by Michael J. Fox), travels to his own future. In it, his future self and future children all exist, whom he could theoretically visit. This is similar to Marle traveling to 2300 and meeting her descendant. The paradox is, if Marty left the timestream, how does he exist in the future?
Here's a little theory of mine that can go a bit towards explaining the paradox:
Consider the mechanics of time travel (from a very simplified perspective). When a traveler decides to travel from time X to time Y, X<Y, there are two possible ways this could work:
1. The traveler leaves the timestream at X, is kept in some sort of stasis, the timestream continues naturally to Y, then the traveler reenters.
2. The traveler moves immediately from point X on the timestream to point Y, without any chance for the timestream to change. He enters the timestream as it would be if he had never traveled.
The first method may actually be feasible in the real world, with methods of stasis and such. But if it can be done by such simple methods, is it really "time travel"? It can't be used to travel to the past, as the methods in CT can. It would be possible for a system like this to exist, of course, if paradoxes like the Ayla paradox didn't act as evidence against it. The second method seems more like actual time travel, and fits in with in-game evidence (at least as far as I can see). Note that those mechanics are nowhere near complete; they differ for jumps to the past and when multiple jumps are involved.