You think this is a problem:
I have seen countless times some merit sources make quality posts in a particular thread and they will go unmerited.
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There is a thread to report unmerited good posts, I hardly see posts of merit sources reported there.
Then the solution is pretty obvious. When you come across a post (from a merit source) that you believe to be good but is not being rewarded with merits, please report it in the "Report unmerited good posts to Merit Source" thread. Problem solved.