The PWA cannot define every single operation that might fall within its remit, so common sense is necessary, and opinions might vary, slightly. Most surveyors would agree that putting up shelves screwed into the PW would not be covered, but (say) cutting a small alcove in it might be. I don't think that many practising PW surveyors would consider that affixing a stud wall to a PW (however deep the fixings are) would be notifiable work. Its the sort of thing that most people would just do without asking their neighbour!
Yeah, I agree and I hope it's just me overconcerning now. The other surveyor hasn't questioned about this wall yet. It was more of me wanting to be 100% sure that I'm 'free' of PWA now. Just don't want my neighbour complains later and involve his surveyor again.