Based on those results, I am going to begin using a multivitamin powder on all prey offered to my ball pythons, whether live, pk, or ft. A light dusting of vitamin powder isn't terribly expensive, and seems worth it to ensure no minor deficiencies in nutrients will occur. If freezing does destroy some vitamins, replacing them with a bit of dust is simple. With some preliminary evidence that it helps, and the fact that it does no harm...why not?
I'm not sure that ball pythons taste their food, but they most definitely smell it, and anyone who has tried to switch a stubborn animal from live to FT can attest that they do indeed detect a significant difference between Live/PK and FT.