What year is a penny rare?

Rare dates for Lincoln cents include 1909-S, 1909-S VDB, 1911-S, 1914-D, 1922, and 1931-S. Then some not as rare but still valuable dates are 1910-S, 1912-S, 1914-S, 1915-S, 1922-D, and 1924-D.