Excell File Won't Restore

Recently I lost some Excel files that are modified every week. This should
be no problem to restore because I backup every week. However, when I try to
recover the file I only get a 10 month old version...the latest one just will
not come up. A look at the actual backup file in my dedicated hard drive
didn't find any of the Excel files that were modified every week. This
suggests that they were not backed up...however, the Vista backup setup
indicates all files (except video) are to be automatically backed up. Anyone
know what went wrong and how to get the Excel file recovery to work?