1 Samuel 14:49-51 tells us that:
49 Saul’s sons were Jonathan, Ishvi and Malki-Shua. The name of his older daughter was Merab, and that of the younger was Michal. 50 His wife’s name was Ahinoam daughter of Ahimaaz. The name of the commander of Saul’s army was Abner son of Ner, and Ner was Saul’s uncle. 51 Saul’s father Kish and Abner’s father Ner were sons of Abiel.
Verse 49 does not record the full number of Saul's sons. Ishbosheth, Saul's ephemeral successor, is missing along with Rizpah's sons viz. Armoni and Mephibosheth.
Some have claimed that they're missing because this verse was written before those sons were born. In order for this claim to stand, Samuel must've been written over a long period of time as 2 Samuel ends with David's death(40-32 years after Ishbosheth's own death). This is a claim that would need evidence besides an oddity in 1 Sam 14:49 to support it.
Additionally problematic about the '1 Sam 14:49 was written before Ishbosheth's birth' explanation is the fact that it would require Saul's daughters, Merab and Michal, to be born before Ishbosheth as they are mentioned in this verse. This is unlikely, as it would require Merab to have grown relatively old before Saul married them off:
- Saul reigned for 42 years(1 Samuel 13:1), a figure that Paul rounds to 40(Acts 13:21)
- Ishbosheth was between 35 and 40 years old when Saul died, depending on when he came to power at age 40(2 Sam 2:10) during the 7.5 years that David reigned in Hebron before he was made king over all Israel(2 Sam 5:5), meaning that 1 Sam 14:49, if written before the Ishbosheth's birth, must've in Saul's 7th year at the latest.
- This solution would then require Merab to be around 20 when Saul offered her up to anyone bold enough to challenge Goliath. While not at all early for marriage in the 21st century, it would've been strange at the very least for a woman, and a king's daughter at that, to be unmarried at such a late age.