[basic.lookup.unqual]/4-6 don't quite use formal terminology for certain things.

A name used in global scope, outside of any function, class or user-declared namespace, shall be declared before its use in global scope.

This defines the concept of "global scope". But where does the line get drawn for being "outside" of a function? Is the "inside" of the function the body of the function definition, or something else? Are the parameters or return values of a function declaration/definition considered "inside" or "outside"? The obvious intent is to talk about the function body (that names in a function body are not in the global scope), but it's not 100% clear.

Similar questions could be asked of class and namespaces.

Paragraph 5 has a different problem:

A name used in a user-declared namespace outside of the definition of any function or class shall be declared before its use in that namespace or before its use in a namespace enclosing its namespace.

Unlike "outside of a function", a function definition is a well-defined construct. However, a function definition includes its prototype: return value and parameters. Again, this is likely intended to mean the body of a function definition.

In paragraph 6, we have:

In the definition of a function that is a member of namespace N, a name used after the function's declarator-id shall be declared before its use in the block in which it is used or in one of its enclosing blocks ([stmt.block]) or shall be declared before its use in namespace N or, if N is a nested namespace, shall be declared before its use in one of N's enclosing namespaces.

The issue here is that return types can appear before the declarator-id, so that needs to be accounted for here.