(1.) The genuine overprint has serifs on the letters "B", "C", and "K". This example does not.
(2.) Exp: do. Ref: Aretz & Johnson.
(1.) The genuine overprint forms an arch. This example is straight.
(2.) In fact, the Scott catalog does not show a straight overprint like this on the 1 centime black stamp.
(3.) Exp: do. Ref: Scott Catalogue