According to David Akers, the die used to strike the reverse of the 1846 half-eagle was also used to strike proof examples of 1844, 1845, 1848, and possibly 1847. It is further interesting to note that two 1846 examples have been issued a "star" designation (the present example not included), and in both cases, it was due to somewhat prooflike quality. Additionally, Doug Winter has noted that some "MS63 and MS64 examples from the S.S. New York which have seawater surfaces." These preliminary observations play a significant role in evaluation of the present piece.First of all, semi-prooflike character cannot be mistaken on either side. The obverse displays a subtle hint of device-to-field contrast, while fine die polish lines sweep upward through the field above the eagle's head. In addition, definition of the motifs is razor sharp, and easily on par with the quality of coins struck fifty years later. It is difficult to imagine that even a proof striking would display stronger definition.
Turning to potential impairments, some of the obverse field is occupied by uneven planchet quality, quite possibly due to "seawater effect" referenced by Winters. The roughness is located mostly just left of the neck and in the lower right field, and were this a large-cent, the artifact would be dismissed as a planchet lamination (which may actually be correct). An effect on luster is noticeable only at certain viewing angles, and if indeed it is a result of manufacture, then of course it should have no impact on grade. NGC has chosen this route and established quality as consistent with the MS-64 level.
At present, NGC's population reports show seven coins graded MS-64, with two of them given the star designation discussed earlier. None are graded higher, thus making this one tied for the finest certified, ignoring the "star" designation and assuming no resubmissions. For the collector of high-end gold type, it doesn't get much nicer than this.