I find these cases strange. Can you clarify theymos?
Read the merit schedule, it does not line up directly with the activity schedule.

Jr with 0 Merit instead of 30
Required merit for Jr. Members is 0, so they get 0 merit.

Hero with 1000 Merit instead of 500
He's eligible for legendary, so he gets 1000 merit.
And is it possible for any existing user to lower their rank because of the introduction of merit? Someone complained about that
No. All users got the requisite amount of merit for their rank automatically.