Whenever I ask call center agents during reservations when they will charge no show fees, they always said that it's charged when the passenger who initially ditched the last segment(s) and then later decide to use them in future. Then the passenger will be charged the no show fees plus the rebooking fees (if the passenger has to change to other flight times). Probably unless a passenger is a frequent offender or such abuses happen on a large-scale among passengers, CX probably may not actively go after the offenders.