Adam Clarke on 2 Samuel 23:13

And three of the thirty - The word שלשים shalishim, which we translate thirty, probably signifies an office or particular description of men. Of these shalishim we have here thirty-seven, and it can scarcely be said with propriety that we have thirty-seven out of thirty; and besides, in the parallel place, 1 Chronicles 11:11-47, there are sixteen added. The captains over Pharaoh's chariots are termed שלשים shalishim, Exo 14:7.

The Philistines pitched in the valley of Rephaim - This is the same war which is spoken of 2Sam 5:17, etc.