I get your point, but how to tell "labelling" from typing? Typing depends on semantics. This particular example only works out because the types are all strings, which is a case of sort of loose typing often used in programming. It could've been like this:

  typedef struct {
	union {
		company_t * company;
		school_t * school;
		project_t * project;
	};
	union {
		address_t * location;
		url_t * url;
	};

etc.