How often do the ticket inspectors come in right after the airport stop? If it's relatively rare, you theoretically could ride that one stop without a ticket (but of course that would be totally illegal, do not do it).
I was there recently for a conference, didn't know about the 9eur ticket and got the 10eur 24 hour ticket for zone ABC on the machine. Anyway, forgot to stamp the ticket, of course. The controller didn't give us a fine but warned us to stamp it before we get to the central station.
I got fined once when leaving SXF, because my ticket purchase in the app went through 20 seconds after departure (I rushed into the leaving train while buying the ticket). So, yes, they do check as early as that.
