The 1940 Proof Lincoln cent is one of the most difficult coins with a Brilliant finish to find with Cameo surfaces. There are less than 5 known 1940 Proof Lincoln cents with Cameo surfaces.
Coins with Cameo surfaces were some of the first coins struck from a fresh pair of dies and planchets. And from 1936 to 1942, very few coins were actually struck from the fresh polished dies and planchets. Therefore, most Proof coins from 1936 – 1942 lack Cameo surfaces.
The only Proof Lincolns cents that do display Cameo surfaces from 1936 to 1942 are the 1936, 1937, 1938, 1940 and 1942. Out of the five different coins that do have Cameo surfaces, the1940 Proof Lincoln is the scarcest of all with Cameo surfaces.
The only two tougher dates for the Brilliant Proof Lincoln cent series that are non existent with Cameo surfaces, are the 1939 and 1942 Proof Lincoln cents.