For 2008, the Mint made a few slight changes to the design of the Silver Eagles. This mostly was a font type change that was fairly minor. It added a serif onto the U in TRUST on the Obv and on UNITED on the reverse. The L in LIBERTY is slightly different. The Tilde between SILVER and ONE on the reverse is different.
On April, 17th 2008, NGC reported that it had discovered a Major Hub Variety. It turned out that there were some 2008-W Burnished Silver Eagles that were minted using the reverse design of 2007. Rick Montgomery, NGC President, comments that "this is a significant hub variety. It has very clear diagnostics, and appears on one of the most widely collected of all US coins." At this point in time, only 2008-W Burnished Silver Eagles have been reported to have this design difference.The easiest way to determine if your 2008-W Burnished Silver Eagle is the Reverse of 2007 is to look at the U of UNITED. The 2008 Reverse has a serif on the right side of the letter; the 2007 does not have this serif. The tilde between SILVER and ONE is another point to look at. The 2008 has a softer tilde that looks more like an ocean wave; the 2007 has sharply upturned and downturned points on either end with the middle being a straight line..
Not only is this coin the most important variety in the Silver Eagle series it is also the rarest mint state Silver Eagle to date. According to a US Mint report issued as the result of a Freedom of Information Act request 16 reverse dies were used to strike 46,318 coins. Some sources report 15 dies were used because one die set only struck one coin. Its also important to bear in mind that the West Point Mint had an abnormally high scrap rate in 2008 among its burnished offerings that ran as high as 50% in multiple instances. While it is not known what percentage of the 2008W reverse of 07 coins displayed the necessary level of perfection to make it past QC and into the hands of the public its certain that less than the often quoted 47,000 coins actually exist.
Examples of this coin that were submitted to NGC in the first 30 days after issue were eligible for the Early Release designation. The combination of a low initial mintage, mild probability of making MS-70 and the very narrow submission window has created a graded population that is exceptionally low. These coins don't come to market very often.