Can an employer rely on a termination clause that was signed by an employee six years after the employee was hired?

In Allison v. Amoco, supra, H.J. MacDonald J. considered an agreement that had been signed by an employee six years after he was hired. The agreement dealt mainly with the obligation of the employee to maintain the secrecy of his work as a seismologist and in addition contained a 30-day termination clause. The employee was dismissed 18 years after the document had been executed. In this case MacDonald J. held that the employer could not rely on the 30-day termination clause. At p. 508 he said: It would seem to me that as neither party considered [the agreement] as designed or intended to do more than to maintain confidentiality, the words dealing with notice were without consensus and that part of the exhibit might be considered non est factum. He held that if it was the intention of the parties to provide for 30 days’ notice of termination after six years of employment such intention must be expressly and clearly stated. In his view such intention was not clear and was ambiguous.