There are exceptions based on the interpretation of the rule. For instance, consider the situation where a promise was made verbally and the promise was breached. In Australian Courts, in order for there to be remedies, it is necessary to prove that the contract itself can be excepted from the Parol Evidence rule. Now some terms of statements in contract could lend itself to ambiguity for instance. Courts interpreting such a contract are forced to admit the extrinsic evidence in order to resolve the ambiguity.
Patent ambiguity situations where the language used could lend it different possible meanings or where another language in the document makes the original one unclear is used, as in the case of White v Australian and New Zealand Theatres Ltd could be reasons for exceptions. Similarly, latent ambiguity situations where a clear meaning does not exist as in the case of Hope v RCA Photophone of Australia Pty Ltd, then the case could claim exception from the Parol evidence rule. Where a doubt is created because of extrinsic knowledge, then the same doubt has to be resolved by using extrinsic evidence.
Ambiguity can also exist because of the identity of parties, or their capacity or relationship. Sometimes, extrinsic evidence would be needed in order to prove consideration as well or there are inconsistencies in consideration etc. In such cases, the Parol evidence rule exception is applied.