More specifically:

Eclipse Series films i.e. https://www.criterion.com/films/2959-a-colt-is-my-passport, https://www.criterion.com/films/27516-come-on-children, https://www.criterion.com/films/12521-sanshiro-sugata - these stand out the most since several actual Criterion Closet picks are from the Eclipse Series, and most (all?) of them lack spine numbers because their cases are slimline and lack spines altogether

Films in similar box sets like The Ranown Westerns that don't have standalone releases, i.e. https://www.criterion.com/films/32211-comanche-station