I fly from Biggin Hill and we have a number of NSA around the airport that we are asked to observe. Skydemon has always been a fabulous help to pilots to understand where these are, as with many other airfields that I fly into. This helps enormously to not upset the airport operators and neighbors. 

However, I have noticed recently that the Biggin Hill NSAs had partially disappeared, particularly the ones outside the ATZ. I have just had a chart update and now most have reappeared and a number of others (not notified by the airport as far as I am aware) have appeared! There remain some others that are still not shown in SD. 

I know this info is not "official" in that it is not in the AIP, but where does SkyDemon get this information to display these areas? I suspect the Pooleys guide as I can see an area truncated in shape as it is by the page margin in the Pooleys guide yet the area extends further North on the Airport's own drawings. I understand that these are 'unofficial" pieces of data and it is a great courtesy that SD have chosen to display this info and is in no way obilged that this info is correct! Just curious as to how these differences are cropping up.