I have an old radiology bill from when I went to the hospital in 2005. We were broke and dirt poor and it went to collections... I didn't even know it went to collections until I saw it on my credit report in late 2006-early 2007.
The lady at the OC said she is going to research it, contact the collection agency and see if they can recall it and cite a filing error and have it set up as a PFD due to the "Filing error". WAHOO!! 
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She is going to call me back friday with her findings to see if its possible! )))))))