Looks like a good case study for MS vs. Weak Strike. These photos IMO make the coin look circulated. There is extensive die wear (the extended outer star points are obvious) but the high points look worn to about the EF-45 level. The greyish, blotchy color is inconsistent with an original MS coin as well.
Maybe it really is a weakly-struck, late-die-state, cleaned and retoned, mint state example. SEGS tends to over-grade coins compared to the top TPGs and they are also less likely to pick up on defects like cleaning. This coin likely will be valued much lower than an example graded MS-62 BN by PCGS or NGC.
You are right that the Classic series is notorious for softer copper alloy that wore quickly and was subject to corrosion. The matron head cents were made from better coining alloy and held up much better. The dates from 1816-1820 in particular are fairly available in no-problem brown mint state condition, with good strikes.