I can't really believe this - if both parties agreed an alternate contract was made orally then the court would effectively rule against both parties in favour of supporting a knowingly false contract?
FWIW the Wikipedia definition, http://en.wikipedia.org/wiki/Four_corners_%28law%29, contrasts sharply with your use and doesn't really seem to speak at all to overwriting of terms by further contracts.
Ah but in practice, they won't agree. One aide will be motivated to claim the oral contract did not exist.
Yes, but that's not what was claimed. Of course if it can't be established that there was any further [alteration of the] contract then the written contract will be relied on. But that doesn't really seem to be the heart of what the Four Corners doctrine is about.
When you have a written contract, any and all verbal contracts or amendments mean absolutely nothing. It's called the "four corners doctrine" and is a pretty universal judicial practice. Written contracts always, ALWAYS supersede any verbal agreements: with a written contract in hand, any mentions of oral discussions are irrelevant and will fall on deaf ears.