I once came across to a bass in a shop in Paris, which had a fingerboard made wider than the neck all the way from the nut down to the end. The seam of the fb and the neck was flush and neat all the way, but the edge of the fb sort of curved outwards from the seam. I have never seen a solution like that before and never after that either, and I regret I did not take any pics. The bass played nice, the neck itself was actually not very narrow, but the fb was about 1 whole cm wider than the neck anyway. It looked peculiar, but this strange feature actually did not feel strange and didn’t have any affect to actual playing.I asked the shop owner about the fb, but he could not tell much about it, nor the bass, which was for sale on commission. The bass was priced about 12 k Euros and was from late 19th century. I figured out that somewhere in the past the fb needed to be replaced and the owner, from a reason or another, wanted to have a bit wider fingerboard without replacing or shimming the neck. The string spacing felt normal and the same spacing would have been possible with a narrower board, too. The shop owner was helpful, though and suggested to provide the contacts of the owner, but since I was not actually intending to buy that bass, I just thanked him and said let’s just leave it a mystery as it was.