Rotation Error 1920D Mercury Dime

I was searching for coins for an individual and came across an oddity. It is a 1920 D Mercury Dime rotated 90 degrees. I have about 30 of those and no others are rotated noticeably. I've heard of 10 degree rotation but this is the most noticeable possible. Any one have any experience or knowledge of this - prevalence, value, etc.?

 

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there are a couple on Ebay. link:
http://www.ebay.com/sch/i.html?_odk...ie&_nkw=Mercury+Dime+Rotated+die&_sacat=41090

 

Those are interesting, but mostly like what I have seen - rotated 10 degrees.

 

Actually, at least the 20D is around 90. It's somewhat confusing because of the pic's but look at the pic's in the slab.

 

Thanks to both - that 1920D is rotated about 90 degrees. Condition is terrible (mine as about G-6) but is a good guide if it sells.