In that case, it means one of the merit sources allocation has been increased by 200 which could possibly be the last merit source that was added to the list since his allocation was initially small (100 plus 200 now 300 total allocation), good development. I think the allocation of those sources that are active in merit distributions should even be increased further instead of asking for more sources, however, it won't be bad if allocation increases and more sources added too. Whichever way, it's all to the betterment of the community

We can only assume but not absolutely sure of which merit source that had their merit allocation increased. In your words, it could be the last merits source that was added, maybe not, but I feel it could be that the admin honored the last month request of the member that a asked for their merit allocation to be increased.
I feel my source merits aren't enough for me right now. I have failed to merit some posts due to lack of source merits. I admit I am the top merit contributor on the
rank-up threads because I love to help people to reach their desired rank. Some of you may take it negatively, but I still love to help them there.
About adding more merit source, some local boards and other general boards are very active with discussions and need merit source. For example, I don't see members getting merit on the altcoin discussion board, it's rare.