1969 United States Proof Set Error?

[Sub2001zero]

I have a 1969-S proofs set still in it original plastic case and paper box. On the half of dollar, has a big mark on it. The color is tan. The plastic case has not been tamper with and all the
other coins have a bright shine. The coin look like some on touch the coin after it was struck and got some on the coin. I thinks it is not an oxidized stain . The coin has a slight ddo IN GOD WE TRUST and Liberty. I have never seen this before, i have many proof set, look at many other at flea market and coin shops. Would the spot on the coin count as a mint error "Cover about 10% or more on the front and 50% or more on back"?


Here is 2 picture to check out the coin and if you need a larger on please let me know http://pg.photos.yahoo.com/ph/sub2001zero/album?.dir=/fb40

 

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[MUD(S.W.A.T)]

I don't think so but what do I know.

Keep @ it and HH!!

 

[gregl01]

Looks to me like tarnish or oxidation. Is this set mint sealed or has someone "resealed" it
I wouldn't call it an error.
Greg

 

[Sub2001zero]

Like i said in the message. The plastic case has not been tamper with and all the other coins have a bright shine and no cracks in the case. It have to see the coin from the picture. I ask some people
where i live and the said there look to be something on the coin. I post here to see what other think about the coin.

 

[scoutjim99]

it is not an error that i know of but definitely curios, the obverse smudge below Kennedy neck does look like a thumb or finger print, the 1960' and early 70 proof set plastic holders are real easy to get in to with out damaging the container,i have busted quite a few to fill my sets ya never know though it nay become a new error