Maybe this version corrects it automatically on save. If not, it would be very bad.. cause no BIOS would ever boot. So you have to correct CRC byte, btw, it is found at offset 0x21.
I added the ""8D 00 00 00 FF" bytes to the custom roms myself. And the 0xFF at the end means this is the end of the subtable, actually these are the two datatypes:
8D 00 = 0x8D = register on PWM controller
00 00 = this is the 6.25mV multiplier (some customs have 0x02 or 0x04 here, if register 0x8D is found)
Some BIOS have them, some not. You can add them, but then you maybe have to resize tables.
But since you also can edit the maximum and minimum voltage (post#3), offset isn't really needed anymore. Take in mind an offset applies all the time, it is also affecting idle voltage.
Don't just flash some 570 BIOS, it has to be modified to fit your card.
Since you have a 470, you have to patch the driver either way. Benefits from a BIOS mod, if you don't need more voltage, would be the possibility to edit memory timings. But since you use it as a secondary card, not really worth it, i guess.