As I understand it "a) " doesn't guarantee they're not fake.
They're not from D'addario, they're from Amazon i.e. It's from an Amazon warehouse, hence it states "Shipper/seller:Amazon".
Also, if another seller has sent a batch of fake strings to Amazon, then they will be mingled with the real ones from D'addario. You are not guaranteed to get the ones that D'addario sent to the warehouse.
Personally, I've not had any problems and the players code checks out, but it is probably safest to buy from a reputable musical instrument retailer as their stock will be the genuine article.