So the Philistines were subdued, and they came no more within the border of Israel: and the hand of Yahweh was against the Philistines all the days of Samuel.
There is another very powerful reason which we reject out of hand any notion, as advocated by some, that these verses should be discarded as an `interpolation.' In the Biblical perspective, events in the far future are sometimes spoken of as if already accomplished; and if one should understand "all the days of Samuel" as an inclusion not only of his lifetime but also of his changing the government to a monarchy, his anointing of Saul, and then of David - if all of that is attributed to Samuel, then it was indeed true in the fullest extent that the Philistines were completely vanquished.  Samuel certainly set in motion the events that led to that accomplishment.