I need to find international prices of airfare for specific locations in the years 2013 and 2014. Please help my boss will kill me if I cannot come up with this info soon!
There seems to be a good deal of confusion and indeed incorrect information about how air fares are priced in the "duplicate" question suggested in the comments, so I shall post a new answer to this specific question.
Historical fares continue to be published and available in the GDS for information after they expire or are manually deleted for several reasons. The main one is that if a ticket needs to be changed at the request of the traveller midway through his journey, it is quite common to have a requirement that the ticket be repriced as though the new itinerary had been purchased at the original ticketing time.
For instance, BA fare LBA-NYC LLW0S4C1 includes the following, very typical provision in the Penalties category of the fare rules:
//CHANGES AFTER DEPARTURE// THE ITINERARY MUST BE RE-PRICED USING HISTORICAL FARES IN EFFECT ON THE PREVIOUS TICKETING DATE. THE NEW ITINERARY MUST MEET ALL THE RULE PROVISIONS OF THE NEWLY TICKETED FARES SUCH THAT THE RECALCULATED FARE COULD HAVE BEEN USED FOR THE NEW ITINERARY IF PURCHASED ON THE ORIGINAL TICKET ISSUE DATE.
Obviously for a travel agent to accomplish this, he needs access to the complete fare tariff as published on the original ticketing date.
Using a tool such as ExpertFlyer, I am able to look up historical fares up to one year in the past, which is probably a fundamental limit of the air fare global distribution system ("the GDS"). I can inquire with the ExpertFlyer team if you are interested, but frankly their response is usually "we just deliver what is available to us in the GDS, we cannot do any more".
An ExpertFlyer subscription is 100 USD per year, but there is a five day free trial. http://www.expertflyer.com
Note that the fare tariff is only one component of a ticket price estimate. You would also need to know the availability in each fare bucket, which varies second by second; as well as the individual traveller's requirements (e.g., requires changeable fares). However, it will give you some idea of what prices people were paying.
Taxes, airport fees and fuel surcharges must be assessed separately.