The written (see the margin) list would enable Gideon to punish the guilty and spare the innocent people. Succoth was governed by a sanhedrim or council of seventy elders (compare Numbers 11:16), with perhaps seven others of superior rank called princes.
Related Commentaries of Judges 8:14
Judges 8:14
14 And caught a young man of the men of Succoth, and enquired of him: and he describedd unto him the princes of Succoth, and the elders thereof, even threescore and seventeen men.