The Screwtape Letters/WMG

Mark Studdock was The Patient.

 * But...he's not dead.
 * Also, Jane did not start out as a devout Christian.

Wormword outranked Screwtape...in some ways.
Which is why he was better informed about the Materialist Magician project than Screwtape.

In the Screwtape-verse, God did not create the devils
It is stated multiple times that they are incapable of feeling, or even understanding, love; and what kind of an all-loving God would create beings incapable of love? This leads me to think that Screwtape's story of His Father's fall from heaven may have something to it -- perhaps Satan was actually a contemporary of God, not one of His creations?
 * From the preface: "Readers are advised to remember that the Devil is a liar. Not everything Screwtape says should be assumed to be true, even from his own angle." Screwtape says that he can't possibly understand love, but this is because he's reneging on repeated previous passages in which he's already quite explicitly acknowledged its existence. A fun little game (being a Muslim I don't advocate drinking games but this is at least a good example of the trope to list for the purposes of the website) is to read the book and play "Spot the instances of Screwtape contradicting himself". Some of them may not be easy to catch on a first reading. I'll give you one hint to start you off: watch for all his uses of the term "life-force" and pay very careful attention.
 * Other points:
 * Screwtape may be worried about other devils reading his mail; if so, he will not publicly admit to knowing anything that could get him in trouble. He may be explicitly denying that he understands love for this reason.
 * It's pretty obvious that having his letters read is exactly what Screwtape is afraid of. At one point, he does warn Wormwood rather urgently to keep them secret, and offers in return to cover for Wormwood in the event of any trouble related to their correspondence; this, of course, is immediately forgotten when Wormwood tries to use passages from the letters to get his uncle investigated for heresy.
 * The devils have a motivation for refusing to admit their status as God's creations. If their Father Below were God's contemporary, or at least in some other way His equal, they might actually stand a chance of beating Him -- so that is what they choose to believe.

In the Screwtape-verse, devils can "reproduce" by shattering.
It's very clear that devils can absorb each other and damned human souls, so why not the reverse process? That would mean some devils are fragments of earlier, shattered devils. This would explain how Screwtape and Wormwood can be "uncle" and "nephew" -- Wormwood is a fragment of some shattered "sibling" of Screwtape's, Screwtape and the sibling both being fragments of some earlier devil. So Screwtape devouring Wormwood is actually a partial re-assembly.