J.A. Brown was one of the first expositers to claim that the "Seven Times" of Nebuchadnezzar were a 2520 prophetic period. He did not arrive at 1914 as you point out.
William Miller's original calculation was based upon the 2300 days of Daniel 8:14. The prophetic 2520 period was eventually added as one of 14 other proofs of this calculation.