Sorry I dont know the answer but there is a member called Sarraceniac who should be able to help you. Search his name and send him a pm.

In my experience, some species of Nepenthes can be damaged by cold, even if the temps don't actually go below freezing. The damage looks much like this.

Hi Gray. I have the same problem with my plant, its roughly the same age, height and has lots of pitchers. However mine is indoors north facing with filtered light. Its been brought inside for the winter but prior to that its was a lovely luscious green. I'm suspicious that it may need more light, humidity(heat pump indoors), or potentially has had too much water. I doubt its a nutrient deficiency as they dont like mineral/trace elements in their medium. Cant wait to put it back in the shade house.