This section is from the book "The Law Of Contracts", by William Herbert Page. Also available from Amazon: Commercial Contracts: A Practical Guide to Deals, Contracts, Agreements and Promises.
The parol evidence rule does not prevent the introduction of secondary evidence to prove the contents of a lost instrument in writing.1 Oral evidence is admissible to contradict such secondary evidence as to the contents of the lost written instrument.2 However, such evidence must always he limited to the contents of the written instrument. Other extrinsic evidence is governed by the rules that would be applicable if the written instrument were in evidence. If the written instrument supposed to be lost is found during trial, further evidence of its contents is inadmissible even if some evidence has already been introduced.3