What you are seeing are just members who are luckily reached a certain rank before the implementation of the merit system requirement during the first quarter of the year 2018. They are given an initial amount of merit based on their current rank when merit system was initialized.
I see that a lot of accounts on the forum have exactly 100 merit and the minimum requirements to be a Full Member.
They have an exact number of merit because they are not actively participating on some discussion or perhaps a mere farming account who doesn't have anything useful to say in the community.
For current members, your initial merit score is equal to the minimum required to your rank. Of that, a certain amount (less than the usual half) is spendable. The spendable amount was calculated based on your current rank and the number of activity points you earned in the last year. A Legendary member who hasn't posted in the last year would still be Legendary, but would not have any spendable merit.