Think real hard about this. Are the initial positions of the planets required to understand and predict their motions?
Take your time on this one.
Your patronizing tone aside, i'll answer it anyway, without hesitation.
OF COURSE THEY ARE! You must define the distance of each of the planets relative to each other and in which plane, you must define their velocities and then define their starting positions at t(0) relative to each other before you "start" your model.
Of course you must know initial conditions. (Hint: for some systems when the force is known and is shown to be constant then you can establish initial conditions from later observations, even when you have incomplete observation. For the life force we know nothing yet. ]
good grief.