Scott 607a, a 1916 inverted surcharge, listed in Scott only recently. It took nearly 100 years to be discovered. This stamp was offered in the recent Nicholas Follansbee specialized Mexico auction and Nick stated in the item description "....this is the first I have seen in 44 years of involvement in Mexican philately." In his email to me, he said that there are 2 or 3 known. (Illustrated the error in top and the normal at bottom.)

