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The blobs you used either came from a local repository or Cydia. An iOS device will not ever accept another device's SHSH blobs. Never.
 
I pulled those 5.1.1 blobs from another iPod 4,1(that came on 5.1.1 original) with iFaith,and used it on my iPod 4th gen.

Lets wait and see if anyone else managed to do this

EDIT:Here it is,mine tethered downgraded iPod 4,1
4rdwe8.png
 
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