<font face="Verdana, Arial, Helvetica, sans-serif" size="2"> (1) 16 segment rule is a SABRE limitation, and since you're booking through AA RTW Desk, you face this limitation. I believe if you book through BA you wouldn't have this issue, and they have more offices throughout your destinations making possible changes easier.
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That's an AA Sabre limit, not a Sabre limit. Sabre can book up to 24 or something.