You caught me in a crabby mood. Take a look at the "O" mint mark. The surface around it is "white-ish" and untoned. That is the luster. Is it blast white and as frosty as a CC dollar? No. Yet, that coin better be in a Mint State slab or my regard for PCGS will just get lower. When it is graded MS, that means the graders thought the coin was original enough to make the grade. The rounded tops of the weakly struck star rays also look original. Wait until the grades are posted.
There is a tiny bit of wear on the shield outline at K8. Even less at K10 (could be strike) and K5 - two tiny bits of the outline moved. The reverse is mint state (no wear on the orb. So I would give it a technical XF45. The reverse plus being a 51O tells me it was TPGed at AU55.
Let's see PCGS MS-64 = Technical XF-45. O M G I think the ANA has failed in one of its stated goals - education.