NCNS means you have a confirmed time and date, arrive there and she is not there. It has happened to me twice in about 5 years and maybe 150 dates. In one case the lady would say she was not NCNS since she emailed me 15 minutes before the date to tell me that since she had not heard from me in the last two hours she was leaving. I say BS since it was a noon date and we had confirmed the previous evening and I had told her I would be traveling in the morning, but whatever.
It is much more common to have a conversation with a lady, pick a time a few days in the future, then when it comes time to confirm the day before, or morning of, the date, nothing. But that is not a NCNS. You could make it into a NCNS if you decided to show up without having confirmed but that seems pointless. With new (to me) ladies, maybe as many as 1 in 4 conversations start okay, but peter out at some point after we picked a day, but before we meet. Something comes up for her, or maybe she is just flaky, or maybe there is something about our interchange that puts her off. Impossible to know, but it happens. As I have said elsewhere, if I am still interested, I will send a follow up email in a week or so saying I am sorry were not able to meet, but am still interested. Sometimes that works, and it all turns out well.
Keep in mind that the ladies have to deal with a lot of assholes every day, and some may make the decision that it is better to just quietly disappear, avoiding any conflict or confrontation, than to say "Sorry, something came up and I can't make it," which opens the door to all sorts of BS, including whining and accusations, as well as requests to make good at a discounted rate.
Anyway, I do find that such things come in bunches - it can happen three times in a month, and then not for another six months. Keep at it and things will get better. You also may develop some sense of what to expect from each lady, and a strategy to deal with the inevitable misses. The first step is to never count on a date happening when it is with a lady you have never seen before. Plan and act like it is going to happen, but don't count on it, if you get my meaning.
And remember that the good ones make it all worthwhile.
zig