I have LHR-VCE-LHR as part of a DONE4 which I am considering not flying (mainly due to having to transfer LHR-LGW and vice versa).

I know there have been discussion about not flying segments and making sure to cancel them with the airline (to avoid a no show) - but I think these have been in the context of dated tickets.

So if one has an open dated xONEx, and the segments in question have yet to be booked onto flights, am I correct in assuming that since there is no PNR for these segments, I can just not book them, tear out the coupons from the booklet, and just turn up for the next segment (LHR-NRT) as if nothing happened? I am not sure what the alternative would be as I calling an airline to cancel a segment which is open dated is just likely to confuse the CSA.

I understand the general terms of carriage that coupons are used in the order they appear. But in the case of an open dated ticket, untill each segment is booked onto a flight/date, there is no PNR. When one books each segment one provides the airline with the ticket number and then presents that ticket at check-in. I understand if I presented a ticket with unused coupons in the book before the one I was attempting to use. But if in the above scenario there are no previous coupons (and the check in agent has no way of knowing whether they were flown or just torn out and thrown out) - so how could it possible be an issue?