Contradiction with Leviticus 22:27
Leviticus 22:27 requires animals to be at least eight days old before being sacrificed, which contrasts with Numbers 18:17 that specifies the firstborn of certain animals as the appropriate offering, without the mention of age.
Leviticus 22:27: When a bullock, or a sheep, or a goat, is brought forth, then it shall be seven days under the dam; and from the eighth day and thenceforth it shall be accepted for an offering made by fire unto the LORD.
Contradiction with Deuteronomy 12:17
Deuteronomy 12:17 states that you can't eat the tithe within your gates, which includes firstlings, contrasting with Numbers 18:17 which assigns the firstborn to the priests, implying their consumption by them.
Deuteronomy 12:17: Thou mayest not eat within thy gates the tithe of thy corn, or of thy wine, or of thy oil, or the firstlings of thy herds or of thy flock, nor any of thy vows which thou vowest, nor thy freewill offerings, or heave offering of thine hand:
Paradox #1
Numbers 18:17 could be seen as inconsistent with later texts that speak of the redemption of the firstborn, like in Deuteronomy 12:6 and later Jewish tradition. In Numbers, some offerings cannot be redeemed or replaced, while other texts suggest they can be. This could create confusion or contradiction about the process of offerings and redemptions.