David and his men went up, and made a raid on the Geshurites, and the Girzites, and the Amalekites; for those [nations] were the inhabitants of the land, who were of old, as you go to Shur, even to the land of Egypt.
The chronology of these final chapters of First Samuel is not stressed in any manner.  Between the death of Samuel  (1 Samuel 25:1) and that of Saul  (1 Samuel 31), a very long period elapsed.  Josephus stated that it was twenty-two years; and although modern scholars question this, the old tradition that Saul reigned 40 years has never been disproved.  These few chapters regarding those final twenty-two years are, in one way, much like the extremely abbreviated record in Numbers of Israel's forty years in the wilderness.  God's purpose here is not to tell us all that happened, but to give us things for our admonition and instruction.