Regarding Sixteen not appearing, it was likely because she hadn't added him through his 'QR code Golden Core Composition'... But why didn't Senior White appear? Senior White had already added him as a friend, and he was even among the earliest to do so.
Senior Seven Lives Talisman, Sage Monarch Seventh Cultivator of True Virtue, Fairy Sixth Cultivator of True Virtue, Daluo Sect's True Monarch Rain Moon, and the other seniors of the 'Nine Provinces Number One Group' all appeared as well. Although they did not join this time's heavenly tribulation, they had all added him as a friend soon after 'Scholar Drunken Spoon' did. Similar to the scholar, because they had added him too late, they didn't get involved in the group heavenly tribulation.
The world had its own principles, yes... but can't it be a little bit more consistent sometimes?
Song Shuhang felt his brain aching.