Albert Barnes Commentary 1 Chronicles 27:7

"The fourth [captain] for the fourth month was Asahel the brother of Joab, and Zebadiah his son after him: and in his course were twenty and four thousand." — 1 Chronicles 27:7 (ASV)

Asahel died before the courses described here could have been instituted. Perhaps the arrangements of David in his later years were based on institutions belonging to the period of his reign at Hebron.