A little over two years ago, a member of this board, Jeff (teza11), posted images from a 1946 edition of the American Card Catalog that had been heavily annotated. There was some discussion on here about who the annotator might have been, but nobody could figure it out, other than the fact that the person seemed to be part of the inner circle of collectors. That thread is here:
Jeff subsequently sold that copy to another collector, Jason, who posted about it on Net54baseball.com. I saw that post but didn't know at the time who the annotator was. However, now I've determined with a high degree of certainty that it was Walter Corson, member of the Card Collectors' Hall of Fame and prominent collector of postcards, baseball, and non-sport cards. Here is my post on the baseball board, with a reply from the current owner showing some more images. I thought members of this board would enjoy seeing it.