The whole deal

When parties enter into a written contract, a key consideration is to put their respective rights and obligations on a definite footing. Occasions arise, however, when the snapshot captured in a document bears scant resemblance to the image one or both parties had in mind. Mechanisms may be available on application to the court to remedy such inconsistencies. But what is the situation where a written contract clearly states that it "constitutes the entire understanding between the parties" in relation to the subject matter of the contract and "supersedes all prior agreements, negotiations and discussions between the parties relating to it", or words to that effect? Such provisions are known as entire (or whole) agreement clauses. Does such language make a contract impervious to rectification?