Hence "the problem" of Rembrandt: the endless debates among scholars as to whether (often well-known, well-loved) works are autograph pictures, collaborations with gifted assistants, "circle of " pieces made in the workshop or by former assistants who had learned to imitate his manner, or "follower of" works produced to satisfy the demand for Rembrandt-type images in his lifetime, by miscellaneous artists.
WSJ: Rembrandt in America | The Cleveland Museum of Art | A Rembrandt of Our Invention | By Karen Wilkin