I had downloaded the Mark IV Parts Mod yesterday, and dragged and dropped the MarkIVSystem folder into the GameData folder of KSP's root directory. Some of the parts were missing. I was redirected to this forum to explain my issue but instead I found a solution in one of the download links provided. I removed the MarkIVSystem from my computer and downloaded again.
Following the instruction of the install, which was to drag the zipped-up GameData folder into the KSP root directory, and not changing any folder names, I was expecting the missing parts to come back. They didn't.
Could somebody who has installed this mod explain how to make these missing parts return to my game, and what I did wrong?