The title is offically the long version, with “Episode VII” in it (this is the actual title used in the movie). Lucas emphasized on the number of the episode for the Prelogy (which were even bigger on prom material than STAR WARS or the subtitles) because it was commercially challenging to release prequel movies (people knew they were going to see “Episode I-II-III” and that the original 1977 Star Wars had become the 4th one in the series). The concept of sequel is easier to understand, so there is no real need to put a number on posters and trailers. The absence of the number on prom material will also help the publicity around the spin off movies, which is a little bit odd (I’m sure mainstream viewers will go see ROGUE ONE and won’t be pleased to discover this is not the sequel of TFA…).