A flexible and reliable delivery state estimator or evaluator is provided for a drug delivery device. The proposed delivery status estimation architecture includes a position sensor that provides a continuous position sensor signal indicative of a current position of a component of the delivery device movable continuously from a first to a second component position, as well as a position discriminator that redefines the continuous position sensor signal to generate an approximate binary input signal on behalf of a state estimator. The discriminator absorbs any difficulty that may arise from a limited reproducibility or enhanced variability of the original continuous sensor signal, specifically including a user-originated signal spread in a movement of a needle protection sleeve of the delivery device.