Jaime Hernandez: In 2008 or 17 years after these coins were struck, someone was fortunate enough to find one of these coins with a 90 degree rotated die error.
There are other rotated dies known for Commemorative coins but they are all considered very scarce. One of them is the 1989-D Congress Silver dollar which has sold anywhere from $1,000 and up to $4,500. There are estimates of anywhere from 50 to 200 coins existing for the 1989-D Congress Dollar.
However, the 1991-P Korean Dollar is a proof version and proof coins are very unusual with rotated dies. Several experts and dealers in errors were estimating that the coin would bring anywhere from $500 and up. While others beleived it would realize about $2500 or more, especially since it was the only reported example during the time. The same coin was later consigned to Heritage in 2008 and it only sold for $805.
As of 2009 I am personally not aware of any other examples of this error turning up. However, this coin went unnoticed by a collector and the odds are that if one was produced, additional examples should also be out there just waiting to be found.