You will have to make sure that the tickets are prioritized correctly in MDE. You can call and ask that it be done, but I would confirm at guest services at the park before you enter the first day. Be sure to check in MDE that it was done correctly after you enter the first time. It should be fine after that, once the correct ticket is "started".
I am assuming you bought the base tickets for the April trip so that you could book park passes? I honestly think that there will be a way to buy more salute tickets for 2021, either increasing the allotment to 12, or having a separate pool of 2021 tickets. But I understand the concern about waiting for either of those things to happen, without being able to book park pass reservations. We used our 6 salute tickets in January, and have another trip booked in January, 2021. I am waiting for a way to purchase salute tickets for that trip. So far only AP slots for park pass reservations are filling, and even then only for dates in the next few weeks. But it's good to do whatever feels most comfortable for you!