The shipment.qvd is becoming from some QVD Maker . and in that QVD Maker you have it as a incremetanl QVD. whenever this QVD is formed from that QVD Maker then the existing QVD is overwrited by the new QVD.
And in the Shipment.qvw you only have to reload that application and it will automatically has the whole refreshed data.
Yes the data is stored within the QVW application in binary format. To verify if the new data is loaded check SUM of any numeric values in your data in QVW applications (for December ) against the data in QVD.. If it matches then QVW has reloaded with December data