Not many EB4Ls with the original pups surviving then
I've always thought that it was the switches that went first. My first Gibson bass was an EB4L converted to an EB0. All four pole pieces wired together. It blew several amps before I got it looked at.
My current EB4L is stock, although I parted one out not so long ago - because I couldn't find the switch - now it seems the 'nighthawk' switches on sale by the
greatdealz people are the right ones (they sell two types - there are pic of them
here)
I suspect there could have been a trial EB0L before they went split headstock, (I don't recall ever seeing one though) whether it left the factory or balanced at all is another matter. But the EB3L (according to the often-wrong shipping figures) came a year later than the EB0L, so whilst still possible, I feel this is less likely.