Numbers 33 seems to be an independent source which attempts to tally up the Wilderness itinerary from the time the Israelites leave Egypt to their arrival on the plains of Moab 40 years later (see Introduction to Numbers 33). Scholars attribute this composition to a later redactional layer from the Priestly source. Moreover, scholars contend that part of this redactional process included inserting itinerary verses into the narratives of Exodus and Numbers so that these earlier traditions, when it was possible to do so, agreed with the itinerary proposed in Numbers 33. The wording of these inserts are near verbatim in many cases.
The children of Israel traveled from Rameses and camped in Succoth (v. 5)
And they traveled from Succoth and camped in Etham which is at the edge of the wilderness (v. 6)
And they traveled from Etham and turned back toward Pi-hahiroth, which is in front of Baal-Zephon; and they camped in front of Migdol (v. 7)
And they traveled from before Pi-hahiroth and passed through the sea to the wilderness. And they went 3 days’ journey in the wilderness of Etham and camped in Marah (v. 8)
The children of Israel traveled from Rameses to Succoth (Ex 12:37a)
And they traveled from Succoth and camped in Etham at the edge of the wilderness (Ex 13:20)
“Speak to the children of Israel that they should go back and camp in front of Pi-hahiroth, between Migdol and the sea, in front of Baal-Zephon” (Ex 14:2)
And Moses brought Israel out from the sea of Reeds, and they went out to the wilderness of Shur. And they traveled 3 days in the wilderness . . . and they came to Marah (Ex 15:22)
Unfortunately this is about the most similarity we’re going to see between Numbers 33 and the itinerary of Exodus–Numbers. After the recording of these initial stops, the itineraries diverge in radical ways. We will explore these divergent itineraries in the forthcoming contradictions.
In the present case, the difference between the “Etham” of Numbers 33 and the “Shur” of Exodus is puzzling. I would chalk this one up to a scribal error. It looks like the “Etham” of Numbers 33:6-7 was attracted into verse 8, to yield midbar ’Etham. The original might have been more like what we find in Ex 15:22—“and they walked 3-days into the wilderness (b’midbar).” One of the reasons in support of this assessment is that having already left Etham on the other side of the sea, the wilderness that the Israelites now enter into cannot be Etham. Noteworthy too is that the wilderness of Etham is nowhere else mentioned in the Bible. In this case Shur is most likely the correct intended place-name—albeit the Priestly tradition knows no Wilderness of Shur!
This is the only discrepancy in the itinerary of Numbers 33 that can be chalked up to a scribal error (if I recall).