On what basis did Paul claim the right to preach in regions beyond others?
Paul claimed the right to preach in regions beyond others on the basis of his apostolic authority, because those areas were virgin territory outside Israel. The Twelve had no ministry outside Israel, so he was not building on another man's labors or boasting in another man's line.
Les explains that Paul hoped, as the faith of the Corinthians increased, that he would be enlarged to preach the gospel in the regions beyond them. Paul did not want to boast in another man's line of things already made ready to his hand. Since Corinth was about halfway west, the regions beyond included Rome, Spain, Great Britain, and later the New World. Paul could not have said this if the Twelve had already covered the Mediterranean area, but they had no ministry outside the nation of Israel. Therefore Paul's right to preach in those regions rested on his authority as an apostle, and every place he went was virgin territory.