Does order of defining classes matter?

[pk1234pk1234dva-a11y]

Suppose you are declaring classes. Sometimes a method of one class returns another class. I wonder, is it needed for the class that is e.g. returned, to be defined before the method that uses it, or is the order irrelevant?

As an example:

PYBIND11_EMBEDDED_MODULE(some_module, m) {
    auto library = py::class_<Library>(m, "Library");
    library.def("FindBook", &Library::FindBook, py::return_value_policy::reference); // signature is say Book* FindBook(int ID)
    // ! declared after FindBook!
    auto obj = py::class_<Book>(m, "Book");
}

This seems to work fine, despite Book being declared after FindBook, where FindBook returns Book*. So it seems that things are resolved in some deferred/lazy way. Still, I couldn't find documentation about this, and perhaps things are only working by chance.

Can I rely on the order of class definitions being irrelevant, as far as return types and argument types go?