Right, I forgot that you did highlight this apparent discrepancy in the theory.
Some say that the mushrikun cannot be Christians because the Christians are designed in the text by "Nasara". Therefore the Mecca/Medina/Kaba frame is right, they were not : go back to the hamster cage then. But 10 years later some say : guys, guys, they are Christians the mushrikun! All is starting again (hahaha!)
Of course there is an explication which explains these issues.
When one cannot explain something it is mainly because the FRAME/paradigm is inexact.
It has to be put aside to find the logical truth explaining what is not logic/rational and understandable like these problems Nasara/Mushrikun in the text.
Copernicus has put aside the Ptolemy Epicycles dogma/frame/paradigm.
Einstein has put aside the Ether dogma/frame/paradigm.
It is exactly the same methodology that must be taken with the Quran. It works.
But it puts aside the religious dogma being the explication of the origin of the text : if it is not the "prophet" (in the Mecca/... frame) who is responsible of the Quran? Who is? Why? When? (hahaha!) this question is impossible to ask for a Muslim. Impossible. That is why you cannot be Muslim and a scholar about it. Because you will never question what it is about the base of your faith (Mecca/Medina/Kaba), even if it has nothing to do with supernatural things.(Mecca/Medina/Kaba is the fundamental creed of Islam : it cannot be questioned.