Sabre can print up to 24 segments on ATB ticket ticket stock (this includes surface sectors). Also, if your agent is issuing ticket on CX ticket stock he will only receive $100.00 commission (max.) on your ticket. Most agents unfamiliar with RTW's find it is not in their best interest to issue these "complex" tickets and only earn $100.00.
Additionally, if you have more than 24 sectors that you want to fly you can have your ticket reissued later for a $75.00 fee after you have begun travel and used up some of the orginal sectors.
Hopefully this has been helpful to you.