ThinkPad firmware upgrade via USB problems

The original method was posted here: https://trisquel.info/en/forum/update-bios-thinkpads-without-win-or-cddvd-drive

I tried to use this method to upgrade a ThinkPad running a "rogue" firmware. Earlier, I tried to upgrade the firmware using official ISO, but bricked the computer because of unknown and unexpected error. The official firmware upgrading utility reported that flashing was completed and prompted me to restart. The computer could never restart, so I had to ask someone to flash a (rogue) firmware image using an external programmer to make it usable.

Yesterday I decided to re-flash the official firmware and prepared a USB media according to the said post. I first converted the ISO image to img format, and subsequently wrote the img file to a USB media with dd. But the computer (running the rogue firmware) didn't boot the PC-DOS system. It simply gave a "Missing operating system" error message. However, the USB media does work on any computers running normal firmware.

I finally "solved" the problem with certain tricks. Now the computer is running normal firmware and I plan to flash coreboot. (Before flashing coreboot, I need to upgrade the EC, and this is why I needed to upgrade the official firmware.) The lessons are: always keep a copy of "golden image" before firmware upgrade whenever possible, should the upgrade failed; and that rogue firmware images can never be trusted.