Despite its apparent severity, the Parol rule of evidence does not negate all prior agreements or statements and does not exclude their use as evidence. A number of situations do not fall within the scope of the rule and therefore are not technical exceptions, so they are better formulated than exceptions (which is not within the scope of a rule). The third and final rule of admissibility is that under UCC 2-202, parol evidence cannot be contradicted by a writing conceived as a “definitive expression” of the integrated agreement, but by (a) a commercial/commercial/performance history and (b) evidence of consistent complementary conditions, unless the letter is a full and exclusive statement of contractual terms. Moreover, the exceptions to the Parol rule of evidence are rightly different from the judicial jurisdiction. Examples of cases in which extrinsic evidence may be permitted in different legal systems are: the importance of the distinction between partial and full integration is relevant to the evidence excluded by the Parol rule of evidence. In the case of full or partial integrations, evidence contrary to the letter is excluded under the parol rule of evidence. However, for partial integration, additional terms to the letter are allowed. For a euphemism, this can be an extremely subtle (and subjective) distinction. In order to enforce a contract, one must understand its conditions in order for parol evidence to be permitted, but a requirement of ambiguity cannot be used to modify, vary or alter the meaning of the contract. The exact extent of the rule varies from jurisdiction to jurisdiction. As a preliminary or threshold issue, the Tribunal can first determine whether the agreement was in fact entirely reduced to a written document or fully “integrated” (in American terminology).
In the case of the State Rail Authority of New South Wales v Heath Outdoor Pty Ltd mcHugh J maintained the Parol rule “no transaction until it is established first” that all terms of the contract are written.  This threshold question also applies in jurisdictions that apply a very strong form of the parol rule, known as the “four-angle rule.” The rule applies to all written contracts, whether written or not. The fraud law is the question of whether there was a contract; parol`s rule of evidence states that, if there has been a written contract, do the parties understand? However, the rule only applies to events that took place before the signing of the disputed treaty. It has no influence on subsequent agreements that could alter the terms of an existing contract. If a full contractual clause does not exist in the terms of the contract in New South Wales, the Parol rule of evidence is a rule of delay of a fully written contract that does not permit the admission of extrinsic evidence and that the contract must be understood in an objective manner.  For the rule to take effect, the contract in question must first be a definitive integrated handwriting; it must be, according to the Tribunal`s judgment, the final agreement between the parties (unlike a simple project, z.B.). To put it simply: (1) If the parties are considering a full integration of the terms of the contract, no Parol evidence is allowed under the agreement.