Helvering v. Horst, 311 U.S. 112 (1940) , is an opinion of the United States Supreme Court which further developed the “fruit-and-tree” metaphor established in "Lucas v. Earl", 281 U.S. 111 (1930) . "Horst" is the leading case that applies the assignment of income doctrine to income from property.
Horst is the case that everyone goes by when applying income doctrine.
Being the leading case it will be the one used as defense of the doctrine in courts, may have been difficult for the system due to context in the statement.