The date on the back or on the head will not tell you anything, it just says when the mold was created. Try the following websites:
http://www.dollreference.com/barbie_menu1.html
http://www.fashion-doll-guide.com/Vintage-Barbie-Identification.html
http://kattisdolls.net/ (this link has more recent dolls, so I don't think the Japan era ones are on there, but check as a last resort if you have time)