Beagle although I am not doubting what you say (in fact I believe it to be correct) I can't see in the link you posted where is actually states that to add a SSEA rating to an NPPL(M) that you need to do it at a licensed aerodrome.
I must admit I find all this licensed aerodrome business a bit silly really. You can do an IMC Rating, a FI rating but you can't do PPL training - strange.