Originally Posted by Clint

This is no longer the case. There's a November 2015 LOA that swaps these definitions for anybody hired after that date.

Classification (CLAS) date "is assigned based on the date a pilot is first scheduled to complete initial new hire training with the Company....is used to determine pay level and the timing of advancement to succeeding pay levels."

Occupational (OCC) Date "shall be equal to their American Airlines, pilot, Date of Hire...All pilots with the same occupational date will be assigned seniority numbers by age, with the oldest pilot receiving the most senior number and the youngest pilot the most junior number. Occupational seniority is used for determining placement on the Pilot System Seniority list and for bidding purposes."