The collecting two tickets at once issue has been culled since the must use reservation number was brought in.
It is the customers responsibility to have the correct ticket. I am guessing a double use on the outbound leg of the return ticket. A return ticket is valid only for travel outwards on from date and can be used anytime till the expiry date
So buy a monthly return ticket on Monday dated for Monday and travel outwards on Tuesday => not valid for travel
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