I’m not sure I can follow.
I am aware of this concept.
In 2018, the stages weren’t called North and South but Mainstage 1 and 2, with the stage on the lefthand side being MS1.
Back then, Ozzy, GNR, Volbeat and Iron Maiden all played on the MS1. Marilyn Manson played on MS2 (on the right).
This unwritten rule of the South Stage always hosting the big headliner didn’t exist until 2022 or something, when they reworked the festival area.
While Manson‘s set took place on the stage on the right, which (geographically speaking) would be the South Stage nowadays, the slot was more akin to today’s North Stage, given that ALL of the four official headliners (the bands listed above were announced as such) played on the stage on the left.
Therefore, I don’t think it makes sense to proclaim Manson a former South Stage headliner, insinuating that he was the main headliner of that day.
Maybe something got lost in translation or I misunderstood your reply. If so, I apologise.