I just noticed this from Jaco's biography on his website:

QuoteHe used money he earned as a paperboy to make another musical purchase. This time, he bought a new Fender Jazz bass. ...

... With his interest in jazz, Jaco also acquired an upright bass. But, it wasn't easy to maintain and he eventually traded it for another electric bass guitar. Later, he would become known for getting an upright-like tone on his fretless electric.

That word "another" explains it, I think. Jaco always claimed that he bought the BOD in a pawn shop for $15 ($4,632 in today's money) while he was working in a boat yard, which is why he had no problem yanking the frets and slathering about nine coats of PolyPoxy marine epoxy on the fingerboard.

That makes sense.
I went and read a bio..it mentions Jaco tossing the bass into the water
on a japanese tour ; was that the B.O.D. ? If so I imagine 9 coats of polypoxy
might keep the neck playable. I wonder if it leeched salt after that


I also learned Jaco played with Cochran, who might have been the inspiration for the Blues
Bros. I wonder if Cochran preferred dry, white toast.