Is being utterly clean and sober for 10 years and then impulsively drinking a half a glass of champagne at your son's wedding and then getting back on the sobriety wagon immediately and sinning no more, is that a "relapse" in the same way that someone who has stayed sober for two days and then goes back to drinking daily for the next 10 years has "relapsed"? Maybe in a sense they are the same, but I would say the first example is someone who has successfully recovered (maybe with a slight bump in the road) while the other is not a success -
hm...i see them the opposite way: the person who impulsively picks up a glass after ten years is anything but "recovered". that, to me, is a relapse. it's not about the amount.
your second example...no, he hasn't succeeded at quitting, but he hasn't relapsed, either. he simply never quit.