As a data point, I had 2 bookings with completely different dates/departure points for the outbound but return on both was for YYZ-FRA albeit a day apart. System auto cancelled as dupe tickets. I called and the cancelled ticket was reinstated bc the agent said they were not duplicate tickets since they aren't on the same date, but system auto cancelled again after 24 hrs. The second agent did say that these would be considered dupe tickets as they're one day apart - though I guess if I were mileage running I could technically fly back and take the evening departure again to Europe the same day - but that's beside the point. I rebooked the flights with 3 days in between and so far no cancellations.