OK, that was completely out of left field for me!
I've just been to check my fretted Magnum III and the fretboard, which I had assumed was ebony, could very well be phenolic instead. That hadn't occurred to me.
So we have an alternate theory that fits the facts. A previous owner wanted to defret the bass but didn't fancy ripping out the frets and filling, so he had the entire board replaced. Since the side dots were already in place, he had the fingerboard dots placed in the same, original positions to match.
Hmmmmm. Works for me.