Wencit's foreknowledge seems to be of a rather limited sort which is inconsistent with all the explanations which I have seen put forward.
So, for example, he knows where to find Brandark and Bahzell when they are tracking the wizards and assassins who have Zarantha, but doesn't show up earlier to tell Bahzell, Tothas, et al. about Baron Dunsahnta beforehand, saving a good deal of trouble.
He shows up exactly when Varnaythus is about to trigger a magical explosion, and does so by means requiring long preparation, but does not intervene earlier to stop the assault on the hunting lodge, which puts Leeana in danger as well as the Sothoii nobles.
He has to retrieve something from Wulfra at considerable risk instead of just anticipating her finding it in the first place and getting to it before her.
He's aware that he and Kenhodan may be attacked but seems to have no certainty how, exactly.
There are other similar examples.
We've been told that gods foresee only probabilities, although they do so better than wizards or dragons: that precise prediction of the future is impossible. Knowing exactly where to place his little toy to prevent Varnaythus centuries in advance is bizarrely precise.
The idea that he has gone back into his own past has two problems: first, we've been told it can't be done, and second, the first version of himself has to have known (and dealt with, without changing the course of events) exactly the same things his present self does, so it just shifts the same problem to his original self. (If he acts differently at many of these points, many others wouldn't take place in the same way or at all, so his prior self would have had to follow the same path without benefit of foresight.)
Sword Brother suggests that the answer is determinable from something which he conceals via a glamour, which rules out a family of spell-oriented explanations.
The effect is like one of there being certain fixed points in a pattern which he can foresee, but only those points, as though there's a private prophecy Wencit is following - but one which leaves some recognisable mark from outside.
