What is the wisdom behind placing the letter waw before the word "thaminuhum" (their eighth) in verse 22 of Surat al-Kahf?

The exegetes (scholars of Qur'anic exegesis) differed concerning the waw (the letter 'و' which means 'and') in the Almighty's saying: (and they say, "Seven, and the eighth of them is their dog"). It was said that it is the waw of verification, coming after recounting their disagreement, and the statement concludes at "seven." It was also said that it is the waw of the eighth, because for some Arabs, the number seven is a complete and perfect number, and this is the dialect of Quraysh. There are similar instances of this in the Qur'an. And it was said that it is a conjunctive waw that entered at the end of their report about the number to distinguish their affair and indicate that this is the utmost that was said about them, and had it been omitted, the statement would still be correct.