The “24-hour rule” and “backup” defenses are myths. Creating a ROM pack for distribution—even for free—violates the right of reproduction and distribution. Thus, a “proper” ROM pack from a legal standpoint does not exist unless it consists solely of homebrew or Sega’s own official emulation releases (e.g., via Steam or Nintendo Switch Online).
A high-quality ROM pack should include these definitive SMS titles: Alex Kidd in Miracle World
remake, which often includes the original SMS ROM file in its data folders.