What is a checking copy comic book?

Here's a fine example of a 1954 Sparkler Comics #119 United Features FILE COPY, CHECKING COPY Comic Book

Checking copy comic books are some of the first ever printed of that comic. They were copies intended for the editors or "checkers" of ad copy. Making sure all ad copy was correct from the sponsors was important, sometimes checking copies would have check marks in pencil on each ad throughout the book confirming that they were correct!