Your DIY-by-GPX Organiser may (or may not) have an available supply of printed brevet cards for you to buy. If you do buy them (rather than virtual ones), you can still submit your proof of passage through your controls, or of completion of your mandatory route, by means of a GPS file.
(When the Organiser puts your ride on the results, he puts it down as a "printed card" one, even though the actual validation was by GPS. He pays AUK either for a printed card, or for the validation, not both.)
(Most orders for Printed Cards are now made by mistake, so tend to get a "Do you really want the printed ones?" enquiry from the Org.)