Does anybody know how L2 and the trading volume wo

Does anybody know how L2 and the trading volume work? I see about 30 transactions after the opening bell and they don't even come close to a 6 million shares but that is what is shown as the volume. I know the MM's don't have to report all share transactions until after the close of the market but I thought that what was reported as L2 trades was reflected in the daily volume and the NON-reported transactions were covered by T-trades at the close of the market.