Thanks for your detail description.
Our Geocoder data is come from some data like TIGER, so it maybe cannot get the best result because the data limitation. I tested your sample Geocoder string, it cannot be found in our newest data and Bing, so I think that's because data reason.
For our Geocoder, because it's based on dbf file and index file, add or update data is very hard, and the index need be regenerated even you modify dbf succeed. So we don't support modify that. But I think you can build a list in your application (I guess you are using desktop edition), before call our Geocoder, you can match in this list, then you can modify it and add the custom data.
Wish that's helpful.