Adaptation First: The OAV was originally released in North America by Central Park Media in 1996. The Manga it was based on wasn't available in English until 2004, when Viz Media started publishing it. Needless to say, a huge portion of the fandom saw the OAV long before ever reading the manga.
Dawson Casting: Of the four leads in the drama, only Yuki Izawa (Kazuya) was actually the same age as his character at the time. The other three were all in their 20s.