Certain martial arts are meant to be passed down to progeny, and hence, they are written down into manuals to be preserved and transmitted down from generation to generation.
But whom did Wong Seung (the creator of the 9 Yum Jen Ging), the creator of the 9 Yeung Jen Ging, and the creator of the Qwai Fa Bo Deen write their manuals for? We know of no apprentices or descendants, and these manuals all ended up in the hands of people who were not directly connected to the originators. Obviously, the manuals were meant for someone because they would not have otherwise been written (the creators simply would have taken their knowledge with them to the grave).