I've had some issues with the Geocoder as well.
My observations in testing
USA.PointAddress/USA.StreetAddress - Scores can very based on address, such as direction missing or not. These results seem to be acceptable.
USA.StreetName - Score is only based on the Street name of address, number is ignored, scores are pretty useless here. For example, if the street name was a perfect match, score is 100, address number ignored.
USA.Postal - Same as StreetName, if zip is a match, 100 score returned, Address number and Street name ignored.
So I would actually check the Loc_name field to see what part of the composite locator provided the result and try to filter that way. Otherwise the scores will amost always be 100 and the Status will almost always be a Match, regardless if the address was actually found.
I was actually thinking about posting this to the geocoder forum. I have a local composite locator we use in-house, but recently decided to use the Esri geocoder as a fallback for unmatched addresses and these issues came up. It has me rethinking of even using the Esri Geocoder in my apps because of the overhead of error checking.
Technically, that Locator, such as the Postal would find a match at 100%, since that's what it's designed for, but it's up to you to filter out the locators. I am unsure if there is a way to tell the service to only use certain locators in a composite locator.