Pandemic Legacy 2 objectives: build 3 supply depots and build 3 new supply depots
Pandemic Legacy Season 2 Rule The "Build 3 Supply Centers" is a "Prologue" card and you should have destroyed it before commencing January. The rule book specifically states: 


  Use the Prologue Objective card during the [prologue] game.


There's a full play log (Warning Spoilers) that never has two build supply centers objectives in play and that is my recollection of the game as well.