Common Carriers, Rules, & Tariffs

Common carrier airlines serve the public using their published tariffs.

American Airlines provides their rules.

Booking Class Availability - Is there a seat available at this booking class?  The fare rule may be in place, but there still needs to be a seat available.

Most airlines publish fares to the Airline Tariff Publishing Company.  Once published to ATPCO, the fares are available to distributors and other airlines.  In Asia, there is a competitor company.  It is possible to purchase a published fare data feed subscription.
This article states fare data "... will cost you a minimum of $35,000 per month, no matter how you slice or dice it, directly from ATPCO..."
This document describes travel agent access to fares via Global Distribution Systems.