When I spoke of retroactivity, I was only referring to errors relating to pensions, the amounts to be paid by federal pensioners. But if you mean someone who applied for Canada Pension Plan benefits late, say at 68 years of age, when he should have done it three years earlier, I agree with you that the benefits should be retroactive for more than one year. In fact, benefits should be retroactive for the entire three-year period for the good reason that the individual in question was really entitled to them. In order to be consistent, when administrative errors occur, retroactivity should cover the entire period.
Where I think it could be difficult not to apply retroactivity would be in cases of disability pensions. Sometimes, the one-year period should be used for reference only, and not as the absolute rule. There are situations where it is obvious the individual has been eligible for over a year.