I unlocked the next set by playing through SSE. I don't know that I did anything specific though. Probably just unlocking enough characters, cause you need some of the hiddens for those events.
You need R.O.B. one of the hidden characters to gain events 21-28 and the rest like 29-41, you need to unlock all the characters first to gain those events, thats how i figure it out... its more easier to play SSE Mode and you can mostly unlock all the hidden characters too.. im playin it on easy too.