procedure TMain.Log(S: String);
begin
 Memo.Lines.Add(S);
end;

  { ... }

const
  Days: Array[0..6] of String = ('Montag',
                                 'Dienstag',
                                 'Mittwoch',
                                 'Donnerstag',
                                 'Freitag',
                                 'Samstag',
                                 'Sonntag');

 { ... }

 for I := Low(Days) to High(Days) do begin
     if Pos(UpperCase(Days[I]), FN) = 5 then begin
{->        Log(Inttostr(I)+':  '+Days[I]);  }
        FileDatum.Tag := Copy(FN, 1, 2);
        FileDatum.monat := Copy(FN, 3, 2);
        FileDatum.Jahr := IntTostr(YearOf(Date));
        FileDate := StrTODate(Filedatum.Tag+'.'+Filedatum.Monat+'.'+FileDatum.Jahr);
// FileDate := StrTODate(Format('%d.%d.%d', [Filedatum.Tag, Filedatum.Monat, FileDatum.Jahr]));

        if Date > FileDate then Result := vfsOlder;
        if Date <= FileDate then result := vfsAktuell;

     end else Result := vfsNoFile;
 end;