Adam Clarke on 1 Samuel 27:6

Achish gave him Ziklag - Ziklag was at first given to the tribe of Judah, but afterwards it was ceded to that of Simeon, Jos 15:31; Jos 19:5. The Philistines had, however, made themselves masters of it, and held it to the time here mentioned; it then fell into the tribe of Judah again, and continued to be the property of the kings of Judah. This verse is a proof that this book was written long after the days of Samuel, and that it was formed by a later hand, out of materials which had been collected by a contemporary author. See the preface.