This might sound crazy… I really struggled with collecting information, however sticking colourful post it notes with the key information, stats or words on your bedroom walls could help. Furthermore, have you tried saying it out loud as you re-read the information or associating it with an image so that you could picture the numbers with the image in your mind?
As suggested flashcards are always a great tool to use to help remember details specific to case studies. I'd also suggest using images or anatations to help remember each case study. Audio recordings of yourself reading through the notes can also be useful, as it will help you passively learn your notes.
Write the case studies on flash cards but make sure you write as little detail as possible. With the statistics it’s okay if you don’t remember the exact number you can say an estimate in the exam. But some of the statistics are generally easy numbers to memorise such as 200,000 deaths.