According to Osho, he can know past lives if he chooses, but he intentionally avoids it, because the present is sufficient. What you are now already carries the imprint of all your yesterdays; transformation happens only here-and-now. Chasing biographies of previous births feeds curiosity, not consciousness. Attend to this moment, and the whole chain of the past is resolved.
He says he could know your past lives, but he doesn’t, because fixing your life now is what truly helps.