Contradiction with Numbers 4:3
Numbers 4:3 lists the age range for those who serve in the tabernacle as 30 to 50 years old, which contradicts 1 Chronicles 26:12 regarding duties among those of the age 20 and upward.
Numbers 4:3: From thirty years old and upward even until fifty years old, all that enter into the host, to do the work in the tabernacle of the congregation.
Contradiction with Numbers 8:24-25
States that the Levites begin their service at 25 and retire at 50, differing from the indication of serving age in 1 Chronicles 26:12.
Numbers 8:24-25: This [is it] that [belongeth] unto the Levites: from twenty and five years old and upward they shall go in to wait upon the service of the tabernacle of the congregation: [to...: Heb. to war the warfare of, etc]
Contradiction with 1 Chronicles 23:24
Mentions the Levites serving from the age of 20, which generally aligns but can be seen as disagreeing on service duty specifics when compared to roles specified in Numbers.
1 Chronicles 23:24: These [were] the sons of Levi after the house of their fathers; [even] the chief of the fathers, as they were counted by number of names by their polls, that did the work for the service of the house of the LORD, from the age of twenty years and upward.