I thought it was a refin only based on the colors I have seen in the old early 80s ad for the SB basses. White, black, red, and blue. I have seen one JJ SB-2 that was very dark midnight blue and looked original. I wonder if this is the lighter blue color from the ads and has just faded, or maybe a custom one off? The neck pocket would prolly be revealing.
I usually play my JJ SB-2 with either both pups on or the bridge only. Last night I was inspired by your SB-1 to switch to the neck pup. Very raw single coil sounds and I was loving it.