In the first four seasons (the first era of My Little Pony: Friendship is Magic), most of the Mane Six each had about an average of 1.5 absences in one half of a season (13 episodes), depending on the season.
Then, as the second era began with Season 5, they got more absences, with Fluttershy literally being the only one to have as much as five absences in one half of each of Seasons 5 and 6.
But recently, things got even worse. So far in Season 7, at least FIVE Mane Six ponies made SIX or more absences in the first 13 episodes! Truthfully, I have no idea why those writers wanted it to be that way.
Should this ever continue? 'Cause I certainly can't imagine this happening any further!