Charles Ellicott Commentary 1 Chronicles 4:42

"And some of them, even of the sons of Simeon, five hundred men, went to mount Seir, having for their captains Pelatiah, and Neariah, and Rephaiah, and Uzziel, the sons of Ishi." — 1 Chronicles 4:42 (ASV)

Went. —Or, had gone (marched). The time of this expedition to Mount Seir is not expressed; but for that very reason it is likely to have been nearly contemporaneous with the events just described. The band of five hundred would seem to have belonged to the clans that had already defeated the Hamites. Neither Ishi (Yish’i) nor his sons are otherwise known. If a totally different expedition were intended, the expression, “and of them—of the sons of Simeon—five hundred men,” would be a needlessly misleading indirect expression for, “And some of the sons of Simeon.” “Of them” can only refer to the clans whose emigration in the days of Hezekiah has been the subject of this section.