You can initiate a GET_FEATURES request by querying or selecting features of a map service. It is possible that the number of features returned is less than what you expected.
There is a limit to the number of features returned from a GET_FEATURES request for ArcMap Services. The default limit is 2000 features.
Unlike ArcIMS Image Services, the featurelimit setting affects all layers of all ArcMap Services. You cannot specify different limits for different layers within an ArcMap Service of different limits for different ArcMap Services.