I do too think its all about the number of times u do certain task. e.g collecting form deep and sparkling mines number of times or making feasts (certain or all) again number of times. Like a counter, once u reach the specified number set for the goal u get to achieve it. Those who have already gotten the explorer trial, I guess they have already done so many explanations that reached the number set for that particular goal, hence they got it.
My opinion so far but I guess time will tell