I was thinking along the far more plausible lines of "Miner One assembles a candidate block, sends that candidate block to Miner Two to work on as well, and for some reason they both start at the exact same nonce/timestamp/extra nonce". Entirely possible and easily done, but would be unusual for two separate parties to mine to the same Coinbase address, and would be completely pointless for two separate parties to knowingly duplicate the same work.