I have several books listed as Author: Unknown in my Adobe Digital Editions. After removing these titles from Digital Edition's library, I have added the authors names to a file with these books, and then added them into Digital Editions, but it still shows Author: Unknown.
I suspect you need to change the author somewhere in the metadata.
Are these DRM books or non-DRM?
If they are DRM, it may be difficult to change.
If they are non-DRM, try using the free Calibre ( http://calibre-ebook.com/ ) instead of ADE;
it has more editing features and is generally a better written program.