A new sign went up about airlines and the exit tax at SJO airport. Posted the photo in the VIP area but here is the list of airlines, the dates they begin to include the exit tax in the sale price and the date of travel they began selling the exit tax for.
American (and US Air) - March 23, 2015 - June 15th, 2015
Jet Blue - April 17, 2015 - June 22, 2015
Avianca, LACSA and TACA - May 15, 2015 - June 30, 2015
COPA - April 22, 2015 - August 1, 2015
Delta - June 3, 2015 - September 1, 2015
No other airlines are mentioned like United or Southwest so no info on them.
So basically if you bought your ticket after the first date for travel after the second date, you just go to the check in line directly, no need to buy the exit tax (a second time).
Here is a link to the pic I posted in the VIP section:
viewtopic.php?f=23&t=47662