What Changed With the Homerpalooza Takedown and County Fair Updates? Update: 9/20 Patch 2

Anyone able to shed any light on what causes the mini events to start? I came back to the game around a year ago having left it during Deep Space Homer, so that event kicked back in at part 4 which is where I'd left it off. I've not got any of the other returning events though. I completed Homer the Heretic and Rommelwood so am only waiting for the Chiliad and Crook and Ladder and obviously would like to complete them.