Abstract: In a system for recirculative precollation copying of a set of simplex document sheets in reverse serial order on a copier providing a choice of precollated simplex or duplex (two-sided) copy sheet copying, more efficient duplex copying without an initial document counting circulation is provided by assuming that the copy sheets selected for duplex copying are non-orientation sensitive copy sheets such as plain paper (rather than special orientation restricted copy sheets requiring consistent inversion for proper output or binding edge orientation, such as sheets prepunched with binder holes, certain preprinted sheets, etc.