I had thought all the mahogany bodies were clear or transparent finishes, guess not. Mahogany is a lot more expensive than ash, alder, or basswood, so it's usually not painted (except on Gibsons). I'm gonna go out on a shaky limb of guesswork and suggest it was a "seconds" mahogany body, got a ding in it during manufacture, or maybe just mismatched color on the pieces, so off to the paint shop it went. I'm surprised to see no obvious primer coat under the black, my 83' L2k has bright blue primer under the black. Were you the first owner? Possible somebody refin'd it along the way? Short of stripping it, you'll never know, and probably don't care. Early L2k's are among the best production instruments ever made IMO, and you have what looks like a unique bass. It's all good.