Adam Clarke on 1 Chronicles 7:2

Whose number was in the days of David - Whether this was the number returned by Joab and his assistants, when they made that census of the people with which God was so much displeased, we know not. It is worthy of remark that we read here the sum of three tribes, Benjamin, Issachar, and Asher, under the reign of David, which is mentioned nowhere else; and yet we have no account here of the other tribes, probably because the author found no public registers in which such enumeration was recorded.