I bought some of the Heritage lots too, and when I saw these markings I started doing some research. It turns out pulps with annotations like you see here originally belonged to sci-fi super-fan Jack Darrow (pen name for Clifford Kornoelje). Darrow was one of the most prolific letter-writers to science fiction and fantasy pulps in the 1930s. One of the pulps I bought contained an original hand-written fan letter by Darrow tucked inside.
Darrow always counted the pages of each story and noted the totals on the table of contents. The numbers on the left indicate his rankings of the quality of the stories. If you look near the back of the issue, you will probably find a coupon filled out by Darrow indicating his three favorite stories from the issue, along with his name and address in Chicago.
Here is a picture of Darrow at the first World Science Fiction Convention (WorldCon) in 1939 in New York. Darrow is in the upper right.
Back row: Myrtle Douglas (aka Morojo), Julius Schwartz, Otto Binder, Mort Weisinger, Jack Darrow.
Front row: Forest J. Ackerman, Ross Rocklynne, Charles Hornig, Ray Bradbury.
What an incredible gathering of sci-fi talent and fandom!
Todd that is really cool! Great research. I know I have one or two books with similar annotations, but I thought much about it. But I have no idea which ones they are now.