Albert Barnes Commentary 1 Samuel 17:12

"Now David was the son of that Ephrathite of Beth-lehem-judah, whose name was Jesse; and he had eight sons: and the man was an old man in the days of Saul, stricken [in years] among men." — 1 Samuel 17:12 (ASV)

This verse and those that follow through 1 Samuel 17:31 are omitted in the Vatican copy of the Septuagint, as are 1 Samuel 17:55–58. The reason for this omission was undoubtedly to avoid the apparent inconsistency regarding Saul’s acquaintance with David (see the note on 1 Samuel 16:21).