When you start 3+ years before the known threshold date, you're giving yourself the best chances at success. I remember flashing BIOSes for weeks in the computer labs at my university.
EEPROM. And there has always been a reflash method for bricked firmwares for all AMI and Phoenix BIOS' as well. Insert disk with firmware, Hold a key, power on.
Once upon a time we got somewhere in the neighborhood of 1200 dell workstations and not a single one failed the bios upgrade. 10/10 would do again