Board Thread:Spoilers!/@comment-26159109-20160301190120/@comment-2153169-20160304025533

They did not finish 521. It is just they moved some shooting moments according to Ginny's press tour for Zootopia. Since Ginny is unavailable for now, they prefered to move on some scenes for 523 where she does not appear and not loosing some time because of Zootopia's promotion. They'll finish 521 this week as they are supposed to. But; for not loosing some precious days, they decided to take some advance on the finale.

Prolly also why they chose to add one another date in their shooting schedule. They prefer to adapt themselves to Zootopia press tour :)