It was on a Mac ROM back then
Well, that explains why it doesn't work in Windows.
If it was dead, why would it even show up on the nvflash at all?
A ROM may be readable but not flashable; that I have encountered several times.
However, I ddn't know that you were working with an already flashed card.
I can't be sure, but it may be that NVFlash wants the ROM erased before proceeding?