Biblical Commentary on the Old Testament, by Carl Friedrich Keil and Franz Delitzsh, [1857-78], at sacred-texts.com
The same phenomena are met with in the detailed account of the Ammonite-Syriac war, Ch1 19:1-2; Ch1 20:3, as compared with 2 Sam 10:1-11:1, and Sa2 12:26-31. In Ch1 19:1 the omission of the name הנוּן after בּנו is merely an oversight, as the omission of the name נחשׁ in Sa2 10:1 also is. In Ch1 19:3 there is no need to alter וגו ולהפך לחקר into וגו וּלרגּלהּ את־העיר חקר, Sa2 10:3, although the expression in Samuel is more precise. If the actual words of the original document are given in Samuel, the author of the Chronicle has made the thought more general: "to search and to overthrow, and to spy out the land." Perhaps, however, the terms made use of in the original document were not so exact and precise as those of the book of Samuel. In Ch1 19:6, Ch1 19:7, at least, the divergence from Sa2 10:16 cannot be explained otherwise than by supposing that in neither of the narratives is the text of the original document exactly and perfectly reproduced. For a further discussion of the differences, see on Sa2 10:6. The special statement as to the place where the mercenaries encamped, and the Ammonites gathered themselves together from out their cities (Ch1 19:7), is wanting in 2nd Samuel. The city Medeba, which, according to Jos 13:16, was assigned to the tribe of Reuben, lay about two hours southeast from Heshbon, and still exists as ruins, which retain the ancient name Medaba (see on Num 21:30). In Ch1 19:9, העיר פּתח, "outside the city" (i.e., the capital Rabbah), more correct or exact than השּׁער פּתח (Sa2 10:8). On אליהם ויּבא, as compared with חלאמה ויּבא (Sa2 10:17), cf. the discussion on Sa2 10:16-17.