Looking at the data, poly 7 uses vertex 15 and poly 12 uses vertex 15. but further down in the normal data poly 7 is indexing to normal data 3 and poly 12 is indexing into normal 5. This is giving you 2 different normal data to the same vertex !!! The latter entry will overwrite the former.
So there is definately a problem with the file, not your calculations
So there is definately a problem with the file, not your calculations