2007-S Sac. mint mark question

In the previous thread I posted about the nice looking Sac.
Link to Sac.
It was mentioned that there was something about the mint mark. I took a picture side by side of the 2006 and 2007 mm.
What caused it to be different from last year? Is that an eroded die or a weak strike? Or something else?
2007 is on the left:
Link to Sac.
It was mentioned that there was something about the mint mark. I took a picture side by side of the 2006 and 2007 mm.
What caused it to be different from last year? Is that an eroded die or a weak strike? Or something else?
2007 is on the left:

CoinsAreFun Pictorials Album
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CoinsAreFun Toned Silver Eagle Proof Album
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Gallery Mint Museum, Ron Landis& Joe Rust, The beginnings of the Golden Dollar
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More CoinsAreFun Pictorials NGC
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CoinsAreFun Toned Silver Eagle Proof Album
.
Gallery Mint Museum, Ron Landis& Joe Rust, The beginnings of the Golden Dollar
.
More CoinsAreFun Pictorials NGC
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Comments
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CoinsAreFun Toned Silver Eagle Proof Album
.
Gallery Mint Museum, Ron Landis& Joe Rust, The beginnings of the Golden Dollar
.
More CoinsAreFun Pictorials NGC
<< <i>anyone care to explain? >>
There was probably some crud in the die to cause some minor yuckieness...!!!.....non technical terms...