Ok so based upon a redress, I can offer you the following: in 2005 a policy change resulted in the replacement of indeterminate engagements of 20 years, with 25-year engagements, around that time CF Mil Pers Insr 05/05 was issued. The rules for TOS administration are contained within CF Mil Pers Insr 05/05, and at the time, those serving on an IE20 were offered the option of converting their engagement to an IE25 or remaining on an IE20.
In 2007, major changes to the CAF pension scheme came into force. These changes created the reserve force pension plan and modernized the CFSA. Unfortunately, none of the publications issued at the time explained the grandfathering rules for members who were serving on an IE20.
As for grandfathering, I point you towards the CFSA: A contributor exercising the option referred to in subsection 19(1) of the Act is entitled to an immediate annuity if
(a) they have completed a 20-year intermediate engagement that commenced before March 1, 2007 and are not serving on
an indefinite period of service;
(b) they have 10 or more years of regular force pensionable service and have reached retirement age;
(c) they are not an officer and have at least 25 years of regular force pensionable service; or