A change can be a material one, even if it was within the general contemplation of the parties at the time of the prior agreement, if they made a conscious decision to leave it out because it was sufficiently complex, or the extent of its impact was unknowable: Stones v. Stones, 2004 BCCA 99. In such a situation, I think it is fair to say that the change is simply too unpredictable to be "foreseen" when the agreement was entered into.
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