Serial numbers that are supposed to be unique aren't necessarily unique. I would guess that the BIOS talk to an EEPROM on the RAM modules rather than to the mem

Serial numbers that are supposed to be unique aren't necessarily unique. I would guess that the BIOS talk to an EEPROM on the RAM modules rather than to the memory chips themselves. It would be very easy for a manufacturer to flash identical contents to every EEPROM in a batch, or with a sequentially increasing serial, rather than bother with a database.