American Airlines Little Trick ...
I noticed this several months ago and it's been confirmed by further observations.
American Airlines charges a $50 fee to allow you to make changes to your reservation. If you can find your same flight at a cheaper, reduced price, you can ask for the difference as a credit, less the change fee.
So, to make it worthwhile, the price drop of your reservations has to be more than $50 to ask for a difference credit.
Because of the change fee, I've noticed American Airlines has been pricing their advanced ticket sales about $50 higher than other competing airlines for the same flying period. Somewhere before the departure dates they will then drop the price to market pricing. Since the market pricing is about $50 cheaper, you are entitled to ask for the difference, but the change fee of $50 makes it a wash. This then permits American Airlines to sell tickets $50 higher than other competitors.
I caught on to the trick and delay my purchase of tickets from American Airlines as long as possible. If I can't get the tickets in time, I go elsewhere.
The other airlines haven't caught on to this clever selling strategy yet.