Metadata download when many books have correct title - but wrong author name

I have a good number of books (~250) that at one time were emailed to my Kindle through Amazon - and apparently the metadata author field is set to the email address that I emailed them from. Some of these books were PDF's that I wanted to go through Amazon's conversion process to make AZW kindle versions of. In any event - I now have these books loaded into a Calibre library and I wanted to use the download metadata in bulk function to get the correct author set for all of them (and also of course get the appropriate tags and covers as well).

Most of these books have the Title field set correctly - some of them do also have the Author appended to the title (so for example the title field in Calibre is "<Book Title> - <Author>". I'm guessing that in these few cases I could use a Regex and do a search and replace to grab the Author from the Title field and stuff it into the Author field. But for the rest of the books (the majority of them) - it seems as though the download metadata doesn't work if the Author field isn't set correctly. (That is to say, a book with the correct title set, but the author field set to 'Unknown" fails to download metadata). Is there a way to force download metadata to only look at the title?

Is there any easy, automated way to do this, or do I just need to go through book by book and do it manually?

Thanks.