Well, for starters, you're not peeing out cranberry juice. Also, it appears to be somewhat of a preventative measure. Once you've got the UTI, however, it does approximately bubkes. It may alleviate the discomfort, which is probably why you think it was cured, but this is like people stopping their antibiotics and just phenazopyridine, which turns your pee orange and makes it stop hurting but doesn't fight the infection. Odds are you've done a small amount of damage to your urinary tract by not taking antibiotics.
I don't know. Would seem like the UTI would come back in a day or so if it doesn't cure it, right? Also, I don't ever drink cranberry juice unless I have one, so I don't know how preventative that could be.
Just because you don't notice it doesn't necessarily mean you don't have one; there's a sort of threshold. It appears that what the cranberry juice actually does is contain compounds excreted in the urine that makes it harder for bacteria to establish themselves in the urinary tract. This doesn't outright kill them, though. In fact, this probably promotes selection for bacteria that can withstand it and may in the long run contribute to making UTIs worse.