Taxes on opendated tickets
 

If one is ticketing a xONEx with all but the first interenational segment open dated, how can they calculate the taxes? eg departure taxes ex-LHR? In my case I have told them I will only be transiting LHR and not stopping. But:

1) how can they be sure since my segments are opendated - do they make a comment in the PNR to that effect? How can I check that I haven't been charged this tax - is it on the ticket somewhere in an intelligible format?
2) if I then change my mind and actually stay in LHR for longer than 24 hrs, but the tax has not been charged on my ticket will this be caught when I check in to depart from LHR?

The assumption is that the taxes will stay unchanged for the period of validity of the ticket. Hence it doesn't matter whether you have dates on the individual coupons or not. The only thing that can make a difference is whether you have a transit (X) or stopover (O) mark next to each departure point. This is sufficient information to calculate the taxes. Actually checking whether the calculation has been done correctly is hard, becuase of all the different elements of "taxes" at different points. However it is the O and X that are used as the basis of the calculation, so if those are correct then you more or less have to assume that the calculation is correct unless there is a glaring error.

Obviously, to minimise the taxes, if you know that you will only transit at some point (and that the taxes are lower for transit than for stopover) then you should get the ticket issued that way. However, if you subsequently change your mind and want to stopover then in principle you would require a ticket reissue (just to change X to O) and you would be charged the change fee (US$75) and the extra taxes (if any). If you don't make the change on the ticket then there is a good chance that this will be spotted at check-in in which case you would probably be forced to go through the reissue process, so you had better not be checking in at the last minute.

The PNR is a record of the reservation, not of the ticket, so with a xONEn ticket you only need a PNR covering up to the first international flight - if the rest is open-dated then they don't need to figure in a PNR.