The real answer is "who cares, rule of cool". We don't even play things in chronological order, like when you play the quest Natah (Uranus) Alad V already has an Infested scar on his cheek, you discover why only on Eris. So the chronological order is: Jupiter Alad V (except Ropalolyst and Disturb) -> Eris Alad V -> Uranus Alad V -> Jupiter Alad V (Ropalolyst and Disturb) -> New War Alad V. What a mess.
With this in mind, you can safely guess maybe you're REALLY killing for good your average Sargas Ruk, that node is simply chronologically after every other event with Ruk involved.
Liches at least have an in-game reason to act like this.
The real answer is "who cares, rule of cool". We don't even play things in chronological order, like when you play the quest Natah (Uranus) Alad V already has an Infested scar on his cheek, you discover why only on Eris. So the chronological order is: Jupiter Alad V (except Ropalolyst and Disturb) -> Eris Alad V -> Uranus Alad V -> Jupiter Alad V (Ropalolyst and Disturb) -> New War Alad V. What a mess. With this in mind, you can safely guess maybe you're REALLY killing for good your average Sargas Ruk, that node is simply chronologically after every other event with Ruk involved. Liches at least have an in-game reason to act like this.