You're right, the version described in the original article in the Scientific American did not have the SPL instruction, but the first "Core Wars Standard" prop

You're right, the version described in the original article in the Scientific American did not have the SPL instruction, but the first "Core Wars Standard" proposal in 1988 introduced it. You can see the different versions collected here: https://corewar.co.uk/standards/ https://corewar.co.uk/standards/