Contradiction with Deuteronomy 2:19
Deuteronomy 29:8 mentions possessing the land of the Amorites, while Deuteronomy 2:19 instructs not to harass or contend with the Ammonites for their land.
Deuteronomy 2:19: And [when] thou comest nigh over against the children of Ammon, distress them not, nor meddle with them: for I will not give thee of the land of the children of Ammon [any] possession; because I have given it unto the children of Lot [for] a possession.
Contradiction with Joshua 13:1-2
Deuteronomy 29:8 records the possession of Amorite land, whereas Joshua 13:1-2 states that much of the land remains to be possessed.
Joshua 13:1-2: 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 Psalm 105:44
Deuteronomy 29:8 speaks of land taken by their might, while Psalm 105:44 describes them receiving lands without labor.
Psalm 105:44: And gave them the lands of the heathen: and they inherited the labour of the people;