Search on MOSS not returning all documents in a SharePoint Library

Question

I have a series of documents (.doc and .docx) in a SharePoint library with the naming convention <Customer> Project 5_6 Proposal.  When I search on Project 5_6 Proposal, some of the documents come up, but not all of them.  For instance, I will see CUST Project 5_6 Proposal but not ACME Project 5_6 Proposal.  However, if I do a search on ACME Project 5_6 Proposal, the document shows up in the search.

Anyone know what the issue might be and how I can fix it?  The end users definitely want all the documents with that phrase in the title to show up.

Thanks!
Olivia Stewart