I have added "clientId" and "dateOfBirth" to the Member index, by adding the following to ExamineIndex.config:

<IndexUserFields>
  <add Name="clientID" EnableSorting="true" />
  <add Name="dateOfBirth" />
</IndexUserFields>

But when I run this code I get no results:

        var dobString = dobDate.Value.ToString("s");
        var sc = ExamineManager.Instance.CreateSearchCriteria(IndexTypes.Member);
        var query = sc.Field("clientID", model.ClientId).And().Field("dateOfBirth", dobString);
        var results = ExamineManager.Instance.Search(query.Compile());

There is most definitely 1 member record with those details.

If I run the following in the Examine section of the Umbraco backend, I get the result I expect:

+clientID:8268100408 +dateOfBirth:"1962-07-01T00:00:00"

So, why is my code not getting any results?