~ It's technically Impossible without being a Merit source.
Have you taken into account the airdropped merits given upon the introduction of the merit system?
I think you've missed this part:
~
Trivia:
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.
If we're to add that to the computation, it's possible for users like @TheNewAnon to send 527 merits without being a source. From
bpip.org, the user has total merits of 1,938 and 938 of which were earned. I don't have time to dig into his posts but I'm assuming he's very active in 2017-2018 which makes him eligible for the 1,000 minimum merits required for a Legendary account.