Complex sentence: Prior to December 2004, each'price drop' started at the guide price (see above)-however, with the removal of guide prices, it is no longer possible to judge how closely the starting prices reflect the true value of products.
Split into simpler sentences: Prior to December 2004 each'price drop' started at the guide price. After guide prices were removed it is no longer possible to judge how closely the starting prices reflect the true value of products.