To this day I don't think anyone (outside of Roland) really knows how the 'LA synthesis' in the D-50 actually works. Unlike Yamaha's work on FM synthesis, Roland didn't file any patents for their LA synthesis technique.
A really interesting fact I found out when I did my own research on the DX7's development was that Roland’s technical R&D director Tadao Kikumoto spent over a year researching Yamaha's FM patents to try and find a way to implement FM without infringement, and even longer trying to find prior art to invalidate the patents themselves. In the end, it was apparently this research that eventually led to the D-50.
Actually, over the years, a fair bit of information has been published over exactly how LA synthesis works. They never exactly hid the details. The problem, of course, is that the details are scattered over dozens of magazine articles, and interspersed with half-truths repeated by well-meaning (but simply wrong) gearheads.
If you're really masochistic there's also the D-50 plugin that Roland published not too long ago. One could always disassemble and/or instrument that to ascertain the exact details... not that it would be entirely necessary since at least one company did, by all accounts, come up with a passable replica of the D-50 as a VST, but immediately got hit by Roland's lawyers because they made the mistake of using the attack samples from the D-50's dumped ROMs.
A really interesting fact I found out when I did my own research on the DX7's development was that Roland’s technical R&D director Tadao Kikumoto spent over a year researching Yamaha's FM patents to try and find a way to implement FM without infringement, and even longer trying to find prior art to invalidate the patents themselves. In the end, it was apparently this research that eventually led to the D-50.