Adam Clarke Bible Commentary

Nine - There are thirteen if we count the four sons of Bath-sheba, and nine without them; and in the second book of Samuel there are eleven, reckoning the above four, and without them only seven. In the book of Samuel probably only those who were alive were reckoned, while the author of the Chronicles comprises those also who were dead in this enumeration. Jarchi supposes that the duplicate Elishama and Eliphelet are those which increase the regular number seven to nine; and that the dead without posterity, as well as the living, are mentioned to increase the number of David's descendants; for, says he, the whole book is written for the honor of David and his seed.