This is just one of the things which bugs me about our whole society: it's a widespread tendency in books, in comics, and in television, that when something is in a series, publishers/broadcasters do NOT inform their customers where in a series a particular title is placed. I look at my Tivo with ten episodes of TBBT recorded, and there's no way to tell which ones I've watched or what seasons they are from.
Haven't these people heard of basic, vital information? This is like selling food stuffs without labelling content and quantity. It's insane and I don't get why it's so widespread as to be near universal.