As I understand the analysis in Leibel v. Leibel, because a will is effective as of the date of death, section 5(2) creates a presumption that an applicant has knowledge of the contents of the will on such date. Given this presumption, an applicant with knowledge at the date of death of a will, and its contents, together with all other facts upon which a claim for lack of testamentary capacity would be based would therefore be fixed with all necessary knowledge as of that date. In such circumstances, the date on which such a claim would have been discovered for the purposes of section 5(1)(a) would be the date of death. The same principle would appear to operate with respect to any claim for undue influence.
I’ve given this issue quite a lot of consideration in the course of drafting a paper on the limitation of will challenges. In short, I don’t think that it does. Statutory limitation periods have always applied to causes of action. A will challenge is not a cause of action. The Limitations Act applies to “claims”, not causes of action, but a “claim” is just a universalized cause of action that functions to simplify the accrual analysis and allow for a general basic and ultimate limitation period. If there’s no cause of action, there’s no “claim”. If there’s no “claim”, the Limitations Act doesn’t apply. Let me if know you’d like a copy of the draft paper; I’m happy to provide it.
The quotation above illustrates the problem. Section 5(2) creates a presumption that discovery occurs on the date of the “act or omission” giving rise to the claim. No act or omission necessarily occurs on the date of death. Indeed, there isn’t necessarily any act or omission at all in a will challenge.
The fundamental flaw in Leibel, and the jurisprudence that follows it, is to understand the Limitations Act as having expanded the scope of the statutory limitations scheme to include all court proceedings. This is wrong: the Limitations Act only expanded the scope of the limitations scheme to include all causes of action (the old Act applied to a closed list of causes of action, excluding some, like certain equitable causes of action, that were limited only by equity).