Proposed resolution:

This wording is relative to N5014.

1. Modify [namespace.std], as indicated:

   Let F denote a standard library function or function template. Unless F is designated an addressable function, it is unspecified if or how a reflection value designating the associated entity can be formed. For any value p of type `meta::info` that represents a reflection of a parameter of F, it is unspecified if has_identifier(p) returns `true` or `false`, and if meta::has_identifier(p) is `true`, then the `NTMBS` produced by meta::identifier_of(p) and meta::u8identifier_of(p) is unspecified.

The wording in [namespace.std] p7 guarantees that reflection of the addressable function can be reliably produced. With the addition of the function parameter name, it is possible to access the parameter name of such functions:

constexpr auto p = parameters_of(^^std::endl)[0];
static_assert( identifier_of(p) == "os" ); // guaranteed?

We should clarify that parameter names used by standard library implementation remain unspecified, by making result of `has_identifier` and `identifier_of` unspecified on reflection of such parameter.