I don't understand what studies you are referring to. Each additional paper should be improving whatever parameter estimates are being made, it makes no sense to only look at one result and ignore all the others.
While they'll all get swept up in meta-analyses, systematic reviews, etc. a huge portion of a paper's citation count can come from narrative sections, where that first paper will reap a lot of citations in "First describe by...", "As established in..." etc.
The Nobel Prize goes to the people who discovered something. Not the people who confirmed that they were right.
The Nobel Prize goes to the people who discovered something. Not the people who confirmed that they were right.