In April 2010, Brian Wagner and Kevin Flynn announced the discovery of a new, second die pair used to strike Matte Proof Lincoln cents in 1909. The new die pair exhibits the following characteristics:
Because of the rarity of this die pair in a year that has been studied intensively by numismatists, Wagner and Flynn believe this was a die pair used in December 1909 to produce 180 Proof coins to either finish Proof sets for this year or to satisfy collector demand.
It will be interesting to see how quickly [after June 14, 2010] additional examples will be discovered now that this die pair is known.
UPDATE: In April 2014, Brian Wagner indicated that, after reviewing every appearance of 1909 Matte Proof Lincoln Cents, he could only find 12 examples from this new, second die pair. Out of 43 1909 Matte Proof Lincoln Cents illustrated on PCGS CoinFacts, only six were from the second die pair.