Like you, my family stayed on-site this past October and has MagicBandss from that trip. We are staying off-site in March and linked our UT tickets through
MDE to our MBs. We have successfully scheduled through Fastpass+ for all the days we have eligible tickets for. I would link your tickets to your MDE account as soon as possible and try to schedule. We didn't expect that it would work for us, but it was a pleasant surprise.