Printed articles having unique data thereon, and flexible substrate printing systems and methods that allow for customization of flexible, absorbent substrates. Customization is accomplished by printing variable data on substrate stock in a single run or production pass such that at least some of the articles in a set of articles contains printed matter different from printed matter on other articles in the same set. The substrate stock can include napkin material, toilet tissue material, paper towel material, or any other similar substrate. One or more print engines are configured to receive substrate stock from the conveyor and print variable matter on the substrate stock. The methods and systems allow for economical and efficient production of small or large customer orders without the need to produce individual printing dies or plates.