I got the events for 603979.SS and 002310.SZ when using the following code.

var identifiers = new[]
{
    new InstrumentIdentifier
    {
        IdentifierType = "RIC",
        IdentifierValue = "600703.SS"
    },
    new InstrumentIdentifier
    {
        IdentifierType = "RIC",
        IdentifierValue = "603979.SS"
    },
    new InstrumentIdentifier
    {
        IdentifierType = "RIC",
        IdentifierValue = "002310.SZ"
    }
};

string[] fieldarray;
fieldarray = new string[9];
fieldarray[0] = "RIC";
fieldarray[1] = "Security Description";
fieldarray[2] = "Dividend Ex Date";
fieldarray[3] = "Dividend Announcement Date";
fieldarray[4] = "Dividend Pay Date";
fieldarray[5] = "Dividend Record Date";
fieldarray[6] = "Dividend Frequency";
fieldarray[7] = "Dividend Rate";
fieldarray[8] = "Dividend Currency";
const string eventType = "DIV";
const string eventConstraint = "Dividend Ex Date";

var request =
    new ExtractRequest
    {
        CredentialsHeader = credentials,
        request = new InstrumentExtractionRequestCoraxStandardEvents
        {
            Instruments = instruments,
            OutputFields = fieldarray,
            Events = new[]
            {
                new CoraxEventConstraint
                {Event = eventType, Constraint = eventConstraint}
            },
            DateConstraint = new CoraxDateConstraintRange
            {
                Start = new CoraxStartDateConstraintStartDate { Date = new System.DateTime(2016, 7, 16) },
                End = new CoraxEndDateConstraintNextDays {Days = 15}
            }
        }
    };

The response is:

"RIC","Security Description","Dividend Ex Date","Dividend Announcement Date","Dividend Pay Date","Dividend Record Date","Dividend Frequency","Dividend Rate","Dividend Currency"

"603979.SS","JCHX MINING MANAGEMENT","7/18/2016 12:00:00 AM","4/19/2016 12:00:00 AM","7/18/2016 12:00:00 AM","7/15/2016 12:00:00 AM","2","0.066667","CNY"

"002310.SZ","ORIENT LANDSCAPE ORD A","7/18/2016 12:00:00 AM","4/15/2016 12:00:00 AM","7/18/2016 12:00:00 AM","7/15/2016 12:00:00 AM","2","0.024","CNY"

For 600703.SS, the last event was on 15 Jul 2016.