How to find original firmware?

Hi, I would like to find the original firmware of my drive. I think it was a Philips PBDV 1640, but I had flashed it to BenQ DW1620 some time ago. While looking through pages for a new update I happened to look at the face of my drive and noticed a “DVD + R DL” printed on it. I had never noticed this before and after scouring through some sites I noticed that the Philips SPD 2400BM looked exactly like my drive. Is it possible I have had Dual Layer drive all this time, which had the PBDV firmware on it and not even known? If so, does anyone know where I can get my hands on the Philips SPD 2400BM firmware to bring my drive up to what it should be?

Many thanks

You will have to take the drive out and look on the label for original f/w.