I don't completely understand though regarding the units.
Air Law is a ground school exam required for the PPL. If I pass and get a PPL done privately and say I want to get my CPL, I do my ATPL at Oxford Aviation, will they skip the previous exams, so in this case, Air Law. I would not have to Air Law again as I already did this during my PPL? What are the differences? Sorry but can you put it in lame mans terms