In November 2010, John Wexler reported a 1955 Doubled Die Cent discovered by Richard Snow with curious abrasions on the obverse and reverse, indicating that operators at the mint may have removed the dies from the press to grind off clash marks. Two incredible scenarios arise: either the press operator missed the doubling of the dies during the abrasion process OR the press operator noticed the doubling and replaced them into the press anyway! The authenticity of the abraded die 1955 Doubled Die Cents has been confirmed by the presence of diagnostic vertical die scratches coming down from the left bar of the T in CENT.
Sources and/or recommended reading:
"1955 Doubled Die Obverse Cent Story Gets Even Stranger" by John Wexler, COIN WORLD, November 22, 2010, pp. 5, 58 and 60