Same!! I am not even talking about key studies, but the ones used as evaluation points- there are so many! I find it really hard to remember names and numbers, but they are everywhere! I plan just making a giant spread sheet where I'll put all the studies by names of researchers, so i can just revise what studies are in what unit, then make a similar one for how the study went.
If you have problems with remembering the content of the study remember the BAMFC, Background, Aim, Method, Findings, and Conclusions, or however you call that list, and just revise them a lot. It helps to think of them as a story and visualize what happened. Good luck!