I guess existing number is less because it is a supplement.
It talk about Schneider trophy in a photograph and text like “Introductory book”.
1962年のAIR TRAVEL誌の付録なので現存数は少ないと思います。
内容は特筆すべきことはなく入門書のようです。THE STORY OF THE SCHNEIDER TROPHY RACE 1913 to 1931
1962 Supplement to THIS WAS AIR TRAVEL
Author: Henry R. Palmer, JR.
Published: 1962 by Superior Publishing Company, Seattle
Pages: 18