Albert Barnes Commentary 2 Samuel 23:39

"Uriah the Hittite: thirty and seven in all." — 2 Samuel 23:39 (ASV)

Thirty-seven in all - This calculation is correct, even though only 36 names are actually listed. The discrepancy is explained because while only two names from the second group of three are recorded, the list in 2 Samuel 23:24 to the end contains 31 names. When these 31 are added to the two groups of three (a total of six), the sum is 37. Joab, as captain of the entire army, stands apart from this list.

In 1 Chronicles 11:41–47, sixteen other names are listed after Uriah the Hittite. These were likely the names of men who replaced those on the former list as they died, or who were added when the number was no longer rigidly restricted to thirty.