''gustave courbet: later paintings'' remains at the salander-o'reilly galleries, 20 east 79th street, manhattan, through feb. 28. it will be at the nassau county museum of art in roslyn harbor, n.y., march 7 to may 29. the paintings from catharine lorillard wolfe's collection remain at the metropolitan museum of art, fifth avenue at 82d street, through mid-may.