DS had the York test, I had the same questions you have about it, now I know why. I think is good if you use it only as a reference, but it can give you lots of false negatives or positives. DS showed an intolerance to little less than 100 of the 113? ingredients tested, trying to cook a rotational diet with so much constraints has been a nightmare and we were not able to make a balanced diet out of the few food he could have. Now that we are in the exclussion diet (for the allergy ingredients only), most of DS' problems are gone. Sure, there is always something that makes you think there's something there (he also seems intolerant to potatoes, bananas, etc), but we have got to a point that I wonder if it is actually better for him to have some of these things from time to time just not to miss the nutrtional value.
My dog had the York test as well (not that I'm paranoid about allergies, it was actually my vet offering the york test (vet version) for my dog what made me decide to go ahead with the York test (why my DS can't have it while my dog can? sort of thing). Anyways, to cut the story short. DThe dog has very simple repetitive diet so it's easier to check on reactions than DS's so, after receiving the results of YOrk test for allergies and intolerances (for the dog), and noting the dog was NOT allergic and slightly intolerant to Turkey, I gave it a bit... poor dog had such a bad reaction that she couldn't even stand up, she kept vomiting bilis for a week. I still can't understand why the test didn't pick up such severe allergy, and that has made me think whether I have been worrying unnecesarily (or not) for so many things in DS' diets.
Hope this long post could save you some money...