The NEC isn't specific. The NEC enables ground plug holes to face up, down, or sideways.
No standard outlet orientation exists. No upside-down outlets exist, then.
The United States instals the ground plug upside down, whereas Canada does the reverse.
NEC code-making committees may reject the proposal for lack of evidence.
In horizontal receptacles, grounding should be on the left and neutral on top. This move is safety-driven.