I was fuming over this same subject on another forum the other week.
I FINALLY bought a black light (man was that scary) soo many stains every where. Half of them I don't remember, so they must have been from animals previous to me living there (the carpet was NOT new). Others that I knew were caused by us and I knew I treated (completely soaked in Nature's Mircale) were still there too!
They say the yellow stains are newer, and the blueish white stains are older, or ones which were adiquitly treated with an enzyme cleaner.
I've been informed by some people that the stain under the black light will always be there no matter what. (I didn't know this to be true, and I'm still not positive.)
I poured Nature's Miracle on a new urine spot, watched it under the black light, nothing happened, I checked it 12 hours later, it had turned from a yellow to a blue shade. So I guess that's all that happens.
As far as smells go (which is my main problem here, with urine saturating the carpet) Sopping up the Urine until the spot is as dry as possible (no more urine comes up onto the paper towel) and then soaking it in nature's miracle until that dries, and then soaking it in distilled white vinager until that dries, seems to do the trick.
I'll smell the Vinager for the next 12 hours or so, but after that the urine and vinager smell is gone.
Try that. =)