1986 Missing Reeded Edge – The inaugural year saw some coins accidentally struck without edge reeding, making them incredibly scarce.
1990 No "S" Proof – A few 1990 proof coins were struck at the San Francisco Mint without the "S" mintmark, creating a highly sought-after rarity.
1995-W Proof – Though not an error, this coin is often grouped with rarities due to its low mintage of just 30,125 pieces, all sold as part of a special set.
Reverse of 2007 on 2008 – Some 2008-W Burnished Eagles were mistakenly struck with the older 2007 reverse design, leading to a major collector frenzy.
Struck on Wrong Planchet – A few Eagles have been found struck on 1 oz platinum or gold planchets, causing dramatic valuation spikes.
Double Strikes – These rare pieces show doubling of the design from an accidental second strike.
Die Adjustment Strikes – Weakly struck coins used to calibrate presses occasionally escape the Mint.
Mule Errors – Coins struck with mismatched dies from other series are extremely rare and can bring six figures or more.