I can only relate my personal experience with a few books. 10+ years ago, when Joe Rainone(whatever happened to him?) was selling the Charles Strong collection of Nedors, I purchased three books based solely on their Gerber Scarcity index. They were Exciting #30, Fighting Yank #5, and Thrililng #33. I don't have my Gerber in front of me, but I believe all three had a GSI of 8(one of them may have been a 7).
All these years later, the Exciting #30 and Thrilling #33 remain not only the highest graded copies, but the only graded copies of each book. The Fighting Yank is one of two graded. These books just never come up.