It is PRE and POST orthographic language agreement.
AO=Acordo Ortográfico (Orthographic Agreement)
Portugal "reformed" the language in an attempt for all Portuguese speaking countries to write in the same manner.
For example: Brazil.
But it has created lots of conflicts among the people.
Basically, the agreement tried to simplify the words. For example: "correcto": in the new agreement they removed the "c" ("correto").