Professor Taylor said something like eating needs to be around 75% (of the original amounts eaten, someone will correct me if wrong) and that exercise is important for maintenance. So it appears if the ND protocol is followed calorie counting counts as a new "set" point is made - this is my interpretation.
A few days ago I read a thread where someone's weight had stalled; to kick start weight loss on LCHF the person increased their fat.
If you either know what you were eating religiously after the ND, it could be 1 element that doesn't work for you, which needs dropping, such as butter, milk, cheese, olive oil, avocodos as examples. You may need to be super attentive once you get back in the 12's and measure weight and foods everyday for a while, you'll nail it permanently, as you stuck to the ND.