King Herod's Song (with the possible addition of Superstar) occurs in-universe, with the Translation Convention applied.I could definitely see the Herod of this continuity writing a song specifically to mock the so-called "King of the Jews"/Christos, and most versions of the performance that I've seen (especially the 1973 film's version) have him doing choreography that barely makes sense even within the boundaries of the Musical World Hypothesis. As for Superstar, that takes place in a message from the afterlife (or in the afterlife, or something), and thus could be part of the awesomeness of heaven. Maybe God just likes to have music up there.
JCS is in the same universe as Oscar Wilde's "Salome"
- The two productions are recounts of the deaths of Jesus and his cousin, John the Baptist, told through the point of views of the people who were to blame. Mostly Judas Iscariot and Salome. And since this is all from The Bible, it could be a safe bet that that Jesus Christ Superstar is the sequel to Wilde's production. Or its Spiritual Successor at the least.