Hmmm, by the time my fiance' had his interview, our NOA2 had already expired but they didn't seem to care. I sent my updated letter of intent to him but in his interview experience, the woman did not even look at it. His interviewer was focused on all the income/money related paperwork.
Still, I always say just do what they ask, hehe. I've not yet heard of an updated letter of intent having to be notarized, but maybe if they specifically asked for it, it's best to do that? I'd say perhaps if it's not too much trouble to just go ahead and have it notarized, it can't hurt. It just makes me wonder if they don't always check to see if NOA2's are expired, and if they do, they need a notarized updated letter of intent? I might be thinking of all this for nothing though!
These are just my thoughts

Congratulations and good luck!!!