Jephthah’s claim that Israel had sent messengers to the king of Edom is supported by Numbers 20:14. But there is no similar support of his claim regarding the sending of messengers to the king of Moab. Jephthah could have easily known this from oral tradition.1
17 Israel then sent messengers to the king of Edom, saying, ‘Please let us pass through your land,’ but the king of Edom would not listen. And they sent also to the king of Moab, but he would not consent. So Israel remained at Kadesh.