File metadata not read after renaming

Hi, I have been so excited to have found out about your great product and at first it seemed to have worked just fine, at least capturing 70 % of metadata. But then I had to rename my files and when I reloaded (after cleaning up everything first), no metadata is read properly. I changed the file naming convention (from whatever to TITLE YEAR but probably because I dont have the hyphen, the naming doesnt fit. But isnt Mendeley supposed to extract metadata from within the file (most of them are books, not papers) rather than just the file name? When I click on the SEARCH by TITLE, it messes it up even worse. I'm also sending some files to the support email. The problem is, I cannot rename all my hundreds of files. Thanks, Kilichan