There is no such thing as "US 1620".
All BenQ 1620 drives (and their clones) are the same, from techical point of view.
The firmware in question will work with all BenQ 1620 drives. Same firmware can also be flashed in corresponding Philips/MSI/I-O Magic... drives.
Follow the link DVD_ADDICT posted above to get the latest firmware for any BenQ DVDRW drive.