Originally Posted by
TransWorldOne
The last segment is YY, which means it can be on any carrier. It doesn't need to be on AA or an AA codeshare. So not having service on AA CUN-GDL shouldn't be an issue.
Of course, if there is conflicting language somewhere else stating all travel on AA-only, the YY wildcard may be trumped.
If you really want this fare ticketed, call a good travel agent to see if it is possible.
The rules allow YY as the last segment only if connecting in Aquascalientes, Zihuatanejo or DF, not Cancún. The routing clearly indicates that to connect in Cancún, one must fly AA Cancún - Guadalajara. The OP is misunderstanding the routing rules.