One World / Trailfinders

Yes, the limit goes down from 20 segments to 16 for all tickets sold after 1 June 08. This is due to an IATA deadline to make RTW tickets universally compatible with e-ticketing technology (i.e. mid-20th century mainframe technology.) No exceptions, and FWIW the same rule change is affecting Star Alliance RTWs, which currently allow more than 20 segments.

One other important part of this is that surface segments count against the 16, so if you were going, say, London - Bangkok, then overland to Ho Chi Minh City, and then fly HCMC - Hong Kong, that would consume 3 segments of the 16, even if it's only 2 flights.

Flights cannot be booked more than 330 days in advance (due to airline schedule publication cycles) but date changes are free under the rules of the Oneworld RTW products. Some travel agents like Trailfinders add their own service charges where the airlines themselves may not - part of the convenience of booking through TAs I suppose. If you change the itinerary (rather than just dates) then the ticket must be re-issued at a cost of US$125 plus whatever admin charges and fees the re-issuing airline or agency may want to add. These fees tend to be pretty standard, but can vary considerably between airlines themselves, with British Airways and Qantas being the most nickel-and-dime prone.

Prices are fixed according to where the ticket is bought and where the RTW commences. No haggling on the base price, but as a smart consumer making a big purchase you should ask and be shown exactly how much you're paying for what.

That pretty much answers my question, thanks for your help!

Cheers