For RTWs originating in Africa you can end in any African city; you don't have to go back to the country of origin. So CPT-LHR...XXX-YYY-xLHR-NBO is perfectly okay and there's no open-jaw segment at the end to be counted.

Thanks for all the help... not only do we end up saving quite a bit by starting from CPT, but tack on around 8k miles with the revised routing (including IPC). Just need to sort out where we really want to go in Asia, and I think we'll be set.

Also, can I just confirm that we will indeed be able to change/reissue paper tickets after June as long as we ticket by then?
We'd probably just use Jan/Feb dates and then move them back to May once we get to August. Also not sure whether I need to wait until we can change the whole trip or can do a leg at a time.

If you just change times, you would not even need to reissue. That would only be necessary if you change your routing.

Sorry to bump this.. had one other followup question.

Looking into our options for getting back to the US after the trip is over. I'm guessing that late july/early august tickets will be running around $800 o/w.
As we're likely going to use miles to get to CPT, I thought of combining this with our return into a AA Oneworld Award. However, I can't figure out if the following is legitimate. Does the LHR-JFK return violate the two stopover rule?
JFK-(o)LHR-CPT//LHR-JFK.

If we can't work it out with miles (or without burning 90k for a o/w award), we'll probably just buy the ticket.

I think that in the case of an open jaw it is the first end (CPT in this case) the one that counts as the stopover city, not the second, but I have not personally tested this. Possibly a bigger problem than that, however, will be the 12 month validity of the ow award from date of ticketing.