When Rose was in lab next to her house (prior to entering the game) she found an image on the large computer terminal depicting Skaia surrounded by 8 planets. I think she assumed it was a different session. Do you think the game knew all along that the endgame would actually have all 8 kids planets in play? Jade has three from the Beta session and Johns return should also bring his planet with him.

The game definitely knew that the session would become an 8 player but Rose probably was looking at a different session since at the time there were several sessions happening.