Mixed-model assembly lines typically rely in intermediate stock buffers to handle disturbances and optimize the car sequence between the main workshops in the plant. The optimization of these buffers is often constrained by installation and production specific rules. In this paper an algorithm for the stock management of buffers with drawers is proposed to handle constraints induced by the production's shift pattern. In particular, the cases where the existing models are not produced in a continuum are considered. The proposed algorithm attempts to maximize the availability of the drawers during change over periods minimizing sequencing violations and ensuring model accessibility at the head of the drawers.