it was weird to see 来年 with a sentence using past tense for a second
Almost tripped me up, too, but they didn't give the option for 'last' on the cards so I got it figured out
English is not my first language, but shouldn't "I bought a calendar for next year" also accepted?
(*Also be accepted)
and yes, you are correct.
Calendars aren't free?
I have bought next year's calendar (not accepted)
I bought next years' calendar.