Luckily I have never been in a scenraio like yours.
But according to the theory it is correct that SAF files will stay in the Siebel FS, even when the record is deleted.
From the top of my head the names of the SAF file consist of the Siebel Table name, ROW_ID and REVISION_NUM (and .SAF).
What you could try to do is to locate the files that don't have a corresponding record in the Siebel Table.
Keep REVISION_NUM out of the filter.
But so far I don't think you can find them with just the attachment title.