Possibly check how many of them played two years ago especially given you seem to be the head Werchter man where a festival has booked the 3 same people the same day two years running. Every Rock am Ring headliner has not been booked for at least 4 years with one two others being at least 8 years. 3 of the top 9 only have played in the last 3 years and two were 3 years and and still not headlining now. Two acts max played significant sets from the next top 9 in the last two years, the others 3 and longer. Hardly a lineup every two years haha