The various schools of Biblical criticism take it for granted that this verse represents a "later addition to the text":
Weinfeld, in his Anchor Bible Commentary on Deuteronomy 1-11 (p. 163), states:
just as Israel did in the land they were to possess. Written from the point of view of the Israelites after they had conquered their land.
Driver, in the ICC on Deuteronomy (p. 38), writes:
As Israel did unto the land of his possession: The words could clearly not have been penned until after the Israelites had taken possession of Canaan. They cannot be referred to the occupation of the trans-Jordanic territory by the 2 1/2 tribes (Numbers 32); for the subject of the verb is Israel, without qualification or restriction, so that the limitation suggested is not admissible.