It has been quite a while but on some other schemes that had used something similar, my boarding pass was also marked. If they don't mark the boarding passes, there may be nothing to stop you. If there are no rules on the Debonair passport then maybe you can double dip legally! There is nothing on Debonair's website to indicate anything to the contrary . . . . and Swissair codeshares on Debonair are not specifically excluded in a long list of codeshares in Swissair's web member guide.

Even my petrol station has taken to stamping my gas receipts when they give me a bonus buck--just so there is no double dipping!