Not being in the Pay Field, I may be taking an overly simplistic view at this, or but perhaps not. I look at it this way. Many of us have served long periods on different Classes of Callout. I spent over six summers in Wainwright, Dundurn, Shilo, Aldershot, and Gagetown on Class A and only one summer in Aldershot on Class B. My Class B was considered Full Time, while all those other summers on Class A was only 1/4 Time. Do I feel ripped off? YES, I do!
To simplify this confusing and sometimes unequal formula of calculating Time Served towards a Pension, I propose that the current system, mentioned here, be scrapped completely. I would do away with that Twenty Year Clause (setting 1985 as the cut off date) and instead allow all Reserve Time to be claimed off of the Pay as indicated on one's T-4 slip. Treasury Board and Revenue Canada issue serving members T-4 Slips for wages earned in Reserves as well as Regs. Create a formula, similar to what they have to calculate your UI (EI) benefits, to create a reasonable payment system by which members can 'buy their Time' towards a Pension Plan.
That way if you wanted to claim 35 years you could, but you must remember that it could become very expensive, and for some not worthwhile, as they would have to pay more into the system than what they will be drawing out in the end. There are exceptions to every rule, for instance, a very well off Snr NCO or Offr may be able to pay a humongous lump sum to buy back their time towards a pension and reek all the benefits. Most others will buy back their time, towards a Pension, through Payroll Deductions. The advice there is to consider it like a loan payment and pay it in as large an amount as you can, in as short a period as you can. (This may be the reason that there was a 20 year cut off date - due to the expense on the member) Remember, a Pte will not be paying as much as a MWO. Your payments will be adjusted to your current rank, so if you are a MWO when you decide to buy back your Time, you will pay back all your time at the level of MWO. That is why it is best to pay it back as quickly and as soon as you can at a lower rank. Your end Pension is calculated on your last/best five years of service at whatever rank/Pay Scale you have in that five years.
The advice to buy back your Prev Service, towards your Pension, applies to the Regs just as much as to the Reserves. Buy it back as soon as you can, and pay it off as fast as you can. If you wait until you reach a higher rank, you are paying higher rates, in the end loosing a lot of cash, as you will receive the same Pension in the end as the guy who paid his time off as a Pte and retires after the same period of service and rank as you.
I hopefully have provided something in these ramblings that makes some sense.