Pinocchio's nose will only grow if he intends to deceive or mislead someone else, not if he makes any untrue or unfalsifiable statements because the intention is for him to learn a moral lesson; no moral lesson involved, no growth. Thus, if he says; "My nose will grow now" nothing happens, also if he says; "My nose will grow and I will somehow benefit from it" it won't grow either because that Blue Fairy won't let the wooden deviant get away with anything.