Abstract: In folded-product production in which a product stream is split up into at least two sub-streams which each run through an associated folding arrangement and are then reunited, it is possible to achieve a high level of user-friendliness and good cost-effectiveness in that at least one sub-stream is assigned a marking arrangement for marking the products passing it, with the result that, upon detection of inaccuracies stemming from the folding operation carried out following the splitting-up action, said products can immediately be assigned to the associated sub-stream, and thus to the folding arrangement belonging to said sub-stream.