I think you can still buy the tickets and use them for up to 30 days, I'd try buying the annual pass with them at the gates of Walt Disney Studios before you go into the park on the 2nd day.
I'm just back after being in France for 10 nights. I had previously had the old classic annual pass which was the entry level one I think it cost about €129 each in 2017, got 2017 and 2018 holidays out of it and it expired last August. Id bought that one over the phone in 2017 and got the paper tickets that get you into the park and then had to exchange for the actual annual passport office. It took an age in the passport office.
I went back this year without the annual pass and decided I'd buy them at the gate. It worked a treat. Went to the ticket desks at the entrance to Walt Disney Studios, furthest window to the right, nobody in the queue. Said I wanted 5 magic plus passes, gave the lady the passports, also had the old annual passes with me and gave her those. She used them to locate us on the system and asked was it ok to keep the same photos, I said yes and due to not having to get new photos taken we had the annual passes printed off quickly and it took just over 5 minutes in total. We were waiting outside the passport office for at least 15 minutes the last time and then were queuing for ages inside, so would recommend buying at the entrance to the Studios.
Also check the different discounts that apply to the Magic Flex and Magic Plus. The 10% restaurant discount, 20% off Buffalo Bills and the Magic hours only apply to the Magic Plus and Infinity so it might be worth the extra €40 if you use those discounts a lot when you are there. That would also cut down on your blackout days.