I could not find a simple answer either but gotten round the problem by loading the filenames into a table. E.g.
SET lc_QvdDeltaFiles = $(gc_OutputDir)DeltaBackUp\$(gc_TableName)_*.qvd;
// List all files in Delta files directory FOR EACH File IN FILELIST('$(lc_QvdDeltaFiles)'); LET ln_NumOfRec = ln_NumOfRec + QVDNOOFRECORDS ('$(File)');
FileTable: LOAD '$(File)' AS FileName, FILESIZE('$(File)') AS Size, FILETIME('$(File)') AS FileTime AUTOGENERATE 1; NEXT File;
FileTableSrt: LOAD FileName, FileSize, FileTime RESIDENT FileTable ORDER BY FileTime desc;
// Pick at the latest file LET LatestFile = PEEK('FileName',0,'FileTableSrt');
You can then ORDER BY anything you want. Solution is clunky but works.