The Saddle Ridge Hoard of gold coins, discovered in northern California in 2013, boosted the population of 1877-S 20s by thirty-four examples, one of which was tied for Finest Known at PCGS MS65. Three others tied for Second Finest honors at PCGS MS64.
In 2009, Brian Koller, a cataloguer for Heritage Numismatic Auctions, reported an 1877-S $20 with a repunched final A in AMERICA (the underlying A leans to the right). Because dies from this period were created using hubs, where all of the design details and letterings derive from a master galvano, an anomaly such as a widely repunched letter is inexplicable. Theories include: 1) the doubling existed on the galvano; 2) dies created from the galvano had repunched A's that were corrected in the dies or resultant hubs (hence the reason thjey haven't been seen before): and 3) a corrected galvano was made and all the old dies were discarded except one or two. Koller considers the first scenario to be the most likely.
Sources and/or recommended reading:
"1877-S Double Eagle Shows Repunched Letter On Reverse" by William T. Gibbs, COIN WORLD, July 13, 2009, p. 82.