I believe the significant difference reflects an actuarial adjustment to pension benefits reflecting legislative changes that were previously made to improve the integration of the CPP and the public sector pension plans. There was a problem with the integration whereby previously, upon attaining the age of 65, public servants actually had their pension benefits reduced. This change was made to correct for that and was one of a number of changes that were made, which included, for example, increasing the share of public sector pensions that employees paid over time to bring it more in line with the historical rate, and going approximately from 30% to where it is now, up to 40%. It was one of a series of changes that were made to better align the public sector pension plans with the reforms that were made to the CPP and that are now taking effect.
On November 20th, 2007. See this statement in context.