NOTE: wow, this got long. sorry!
NOTE: I'm English, don't knock my spelling of 'Theorise'!
The line of argument that goes 'The Chrono series was not planned out fromt the start, and so any theories made regarding the overall structure of the universe are irrelevant,' has already been replied to a number of times...
I'm not so sure about a reply along the lines of people can take away their own interpretation of the game and nobody is truly right... that seems to be against the spirit of the Compendium - which does seem to strive for finding the answer which is 'right'.
But I think the answer is quite simple. What we have, in CT and CC are a complex series of events. That much anyone can agree on. Now. The objection above states that because none of these events were planned out meticulously to work along a certain set of rules, then it's useless to theorise.
This is nonsense. Here's an argument
1) For any given group of events, they can either exist together consistently or not.
2) So, the events in the Chrono series can either exist together consistently or not.
3a) For any series of events that can exist together consistently, there is at least one possible set of explanations of their consistency.
3b) For any series of events that cannot exist together consistently, there is no possible set of explanations of their consistency.
4) So, if the events in the Chrono series can exist together consistently, then there is at least one possible explanation of their consistency.
4b) And, if the events in the Chrono series cannot exist together, then there is not possible explanation of their consistency
---
Now...
We want to say that the events in the Chrono series can exist together consistently. And if so, there is at least one way of explaining that
whether the writers had it in mind or not.
Now, the more sophisticated objection to this is:
"Sure, okay, so there are ways to explain it even if the designers didn't know it. But you said it yourself ... there's at LEAST one possible set of explanations. Which means there could be MORE than one. And if the designers don't favour any particular one, then it doesn't make sense to say that one explanation is better than another, or more correct."
This seems true to me, but the theoriser can still reply to this objection along these lines...
"Firstly, even if there are multiple possible explanations, then that doesn't rule out the ability to eliminate the impossible objections. Ambiguity can be good, but theorising is still useful to throw out the impossible explanations."
And...
"Secondly, this is a complex series of events - very complex. In such a case, it is actually pretty unlikely that there is more than one set of explanations that is both possible AND plausible.
What I mean by plausible, is that it generally fits in with what we already know about the universe, and doesn't add anything ad hoc in order to explain things. In other words, an explanation which, given what we know about the universe, we have a good reason to go for.
A possible explanation for the events in the Chrono universe might be that the whole thing was the playing out of a story made up by some random guy which means that any contradictions don't particularly matter - because even within the constraints (or frame of reference if you prefer) of the game world in this case, everything would be made up (as opposed to the usual situation, where a game world in which the things that happen are, within that game world, actually supposed to be happening). But this explanation is not one that is particularly plausible because nothing we know about the game universe adds any support to this explanation."
And...
"Even if you go on to insist that there could still be two or more plausible and possible explanations, then consider what I just said about the implausible explanation and apply to the plausible ones: it it's at least probable that one of those theories is going to be better supported by what we already know about the game universe: even if neither of them have any negatives against them, one will probably have more positives for them."
-----
More sophisticated objecting still might be that this introduction of the concept of plausibility illegitimate:
"Look, why does it matter if an explanation is supported by the events in the story? If the designers didn't have an explanation in mind, then it's just a coincidence that one is supported more by what we know about the universe."
reply:
"Indeed it is... but that doesn't change the fact that such an explanation, one that is supported heavily by what we already know about the universe, and doesn't rely on as much unfounded speculation or ad hoc elements will ultimately be a more satistfying , a more rewarding explanation to all who hear it... and isn't that what we're aiming for? A satisfying set of explanations?"
Conclusion:
Theorise away!