Ecuador 1930 10s Black Mendez Airmail with Black Overprint Error VLM Mint. Scott C34 var

The scarcest stamp in the 1929-1944 airmail series. The regular Mendez Bogota-Quito overprint of 1930 was printed in red-brown ink with a print run of 5,000. However, one sheet of 100 only was overprinted in black. A very difficult stamp. Unlisted in Scott, Sanabria 50. Two expertization signatures on the reverse.