i know shenmue 2 has some Secret events, like the duck racing, shopgirl fight and birthday scene etc.
I am unsure if it is possible to do all of these events in one play through as events need to be done by doing certain things on certain days .. so you would probably not be able to hundred percent complete it (?)
check here for a list of hidden stuff
http://www.ign.com/faqs/2002/shenmue-ii ... faq-362531