std::tuple's allocator-extended constructors say "Effects: Equivalent to the preceding constructors except that each element is constructed with uses-allocator construction". That's not true for the first one, as shown by:

#include <tuple>

struct X { explicit X() { } };

std::tuple<X> f() { return {}; }
std::tuple<X> g() { return { std::allocator_arg, std::allocator<int>{} }; }

The function f() doesn't compile because of the explicit constructor, but g() does, despite using the same constructor for X. The conditional explicit-ness is not equivalent.

Also, the editor requested that we change "implicitly default-constructible" to use words that mean something. He suggested "copy-list-initializable from an empty list".