A more complete explanation came to light with the discovery of the Dead Sea Scrolls: although not present in either the Septuagint or masoretic text, an introductory passage, preceding this narrative, was found in a copy of the Books of Samuel among the scrolls found in cave 4:
The discovery of the Dead Sea Scrolls provided additional information about the narrative, although it wasn't included in the Septuagint or masoretic text. An introductory passage preceding this narrative was discovered in a copy of the Books of Samuel among the scrolls found in cave 4.