Contradiction with Joshua 11:8
This verse suggests that Joshua was successful in defeating the kings and taking their land, implying that they were not yet defeated by Joshua 12:23.
Joshua 11:8: And the LORD delivered them into the hand of Israel, who smote them, and chased them unto great Zidon, and unto Misrephothmaim, and unto the valley of Mizpeh eastward; and they smote them, until they left them none remaining. [great Zidon: or, Zidonrabbah] [Misrephothmaim: or, Salt pits: Heb. Burnings of waters]
Contradiction with Joshua 13:1
Indicates that there were still remaining lands to be conquered, conflicting with the notion of full conquests listed in Joshua 12:23.
Joshua 13:1: Now Joshua was old [and] stricken in years; and the LORD said unto him, Thou art old [and] stricken in years, and there remaineth yet very much land to be possessed. [to...: Heb. to possess it]
Contradiction with Judges 1:1
States that after Joshua's death, the Israelites still needed to inquire of the LORD for guidance on further battles, suggesting not all kings and regions were conquered.
Judges 1:1: Now after the death of Joshua it came to pass, that the children of Israel asked the LORD, saying, Who shall go up for us against the Canaanites first, to fight against them?
Contradiction with Judges 2:21
Shows that God allowed some nations to remain unconquered to test Israel, conflicting with a complete conquest implied by Joshua 12:23.
Judges 2:21: I also will not henceforth drive out any from before them of the nations which Joshua left when he died: