Jon Peterson tracks down the rules that may have been true origin of the “Fantasy Supplement” in Chainmail.

This proves that at least one of the two authors of Chainmail received and studied the very issue of the Courier containing these fantasy rules at the time, and surely could have shared it with his co-designer. Although these rules came out not long before Chainmail, we know from Gygax’s own account that the Fantasy Supplement was a last-minute addition to Chainmail: he later called it an “afterthought.”