So Sharon, Simon, Louis and Kate joined the show, then Kate and Louis left. Dermot, Dannii and Brian joined -but plot twist: Brian leaves and Louis returns. Sharon then leaves the show, Cheryl joins. All is well for a while, all is stable and there is a solid panel. But then Dannii, Simon and Cheryl all leave (Cheryl and Simon join the American version, Cheryl for all of 5 minutes. Dannii joins the Australian version for a few years). Gary, Tulisa and Kelly join, Kelly leaves. Nicole joins. Tulisa leaves. Sharon comes back, but then Sharon leaves, Gary leaves and Nicole leaves. Simon comes back, Cheryl comes back and Mel B joins. But then Mel leaves and Louis leaves. Then Dermot is gone, Caroline and Olly are in. Nick and Rita arrive, but then Caroline, Olly, Nick and Cheryl are all out. Now Dermot is back and it looks as though Louis and Sharon are coming back too.

Now, can anyone disprove that they don't just put 20 or so names into a hat each year and pull out 5 or 6 names?

Now that you mention it, it is like musical chairs with the producers pulling the chairs away so to speak.

yeah it is