Fascinating.
Although I must confess that I don't find finishes a particularily good way to date instruments, especially in the absence of factory documentation and a reliance on catalogs.
This page, using Guild catalogs, states that the JS bass with the walnut finish was not introduced until 1973. However I have a '71 JS II with a walnut finish. Even though I bought it off a rack in a music store, maybe Hans can help me concoct a story that makes it a prototype of the walnut finish and thus worth even more