AdWords Api returns different number of results than requested in query

[Confused AdWords Guy]

I'm working on a C# application using the Adwords .NET library to determine search rates for potential campaigns.

All seems to work well, except that some search queries don't return a SEARCH_VOLUME result.

using System;

using Google.Api.Ads.AdWords.Lib;

using Google.Api.Ads.AdWords.v201710;

namespace WpfApp1

{

    internal class MyClass

    {

        public MyClass()

        {

            AdWordsUser user = new AdWordsUser();

            TargetingIdeaService targetIdeaService = (TargetingIdeaService)user.GetService(AdWordsService.v201710.TargetingIdeaService);

            TargetingIdeaSelector targetIdeaSelector = new TargetingIdeaSelector();

            targetIdeaSelector.ideaType = IdeaType.KEYWORD;

            targetIdeaSelector.requestType = RequestType.STATS;

            targetIdeaSelector.requestedAttributeTypes = new AttributeType[] { AttributeType.SEARCH_VOLUME };

            var locationSearchParam = new LocationSearchParameter();

            var searchLocation = new Location();

            searchLocation.id = 2840; //United States

            locationSearchParam.locations = new Location[] { searchLocation };

            targetIdeaSelector.paging = new Paging();

            targetIdeaSelector.paging.numberResults = 600;

            targetIdeaSelector.paging.startIndex = 0;

            var relatedQuerySearchParam = new RelatedToQuerySearchParameter();

            relatedQuerySearchParam.queries = new string[] { "amherst properties" };

            targetIdeaSelector.searchParameters = new SearchParameter[] { locationSearchParam, relatedQuerySearchParam };

            var targetIdeaPage = targetIdeaService.get(targetIdeaSelector);

            Console.WriteLine(targetIdeaPage.totalNumEntries);

        }

    }

}

Output: 0

In my real application, there's around ~500+ queries per request to help prevent Rate issues. Since the api doesn't error, and simply doesn't return a value, I have no way of knowing what one failed and it causes my lists to be different lengths.

Is there something I should be aware of in-terms of things that shouldn't queried, or some way to handle this situation?

Thanks