There should be no need to use them this year. I am currious about how you ended with two sets. Last year I upgraded and kept using my gold through the end of the year then they switched it to platinum st the gate on my first trip this year.
I bought them from Canada's Wonderland. Exchange rate FTW! Basically amounts to a free drink plan. I couldn't "renew" from my KD Gold (I tried). Not sure but I'd think you'd get a new card even if you upgraded at KD seeing how it's platinum and not gold? I did get the pass processed at KD no problem, in case you were wondering. You don't have to process it at the park you purchased it. When I did that, I didn't go into the park with the platinum passes, because I didn't know if we'd get our free drinks or not, so we went in with the Gold passes.