Firmware images usually have checksums. Was this an Intel blob suffering from bitrot, or does Intel have some more or less error prone way to build your own FW images for NICs?
I suspect NICs these days are tiny computers in their own right. As a motherboard manufacturer, you can probably program them to do all sorts of nifty, with the possible downside of strange things happening if you get it wrong.
It is not the firmware that was corrupted. It is the EEPROM that was incorrectly programmed.
The EEPROM is typically 4kB on the 82754. When it is reprogrammed either by the end-user (eg. via ethtool(1)) or by the manufacturer, the programming procedure recomputes a checksum on the first 128 bytes IIRC (when reprogramming via ethtool, the kernel driver e1000e is responisble for automatically updating the checksum.
So all in all, no, the packet of death issue was not caused by bitrot.
