For tickets issued prior to December 19, 2004:
The customer may receive a refund by accepting a travel voucher or MCO for the difference between the two fares to be issued in the passenger's name. No change fee applies.

For tickets issued on/after December 19, 2004:
The customer will receive the difference in the fares less the applicable change fee in the form of an AA travel voucher or MCO.
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Travel Agencies and Rollovers:

For both Domestic and International itineraries, Travel Agents to indicate “rollover” in the ticket endorsement box. Travel Agents may issue a non-refundable MCO for the residual amount (applicable fees apply for the exchange and may be deducted from the residual). The MCO must be made payable to AA for transportation only and show "non-refundable, valid AA only" in the endorsement box.