Minor spoilers I guess, but Chapter 408 completely changes the timeline. As per Morena's words, she was born in 1998, and the current year is 2021. We could perhaps assume that Kakin uses a different calendar, but this is... a problem (I mean, Nobunaga is obviously not 50 years old).
I think I would use the current timeline and create notes for both Morena's birth and he last Carneval specifying that either a retcon has occurred, or that Kakin uses a different calendar.