i have done some 30 RTWs and once i started, i never had any problems changing dates ( changing routes i had plenty, however), some (few)times i did not even call anybody at all and just made a reservation for the next flight once i knew when i would need it, sometimes not even on the same carrier.
t&c clearly say that the ticket is good on any *A carrier, bookingclass i.e. "A" is flexible; maybe i don't get the OP's issue or i got extremely lucky a couple of times...