Although the people at vgmdb.net don't seem to believe me, the track called "Kidney Stage" on Shooting Battle II corresponds to "Slash Fighter" from Salamander (Lifeforce). Slash Fighter can be found on Salamander ~Again~ (track 12), for comparison purposes.
I'm not sure why Konami changed the name. It's possible that because they used the American name (Lifeforce), rather than Salamander, they felt they could call it 'whatever'. If the name were actually "Kidney Stage", then that would have been listed on Salamander ~Again~. And thus we have an inconsistency.
This is no where near as mysterious as what J.D.K. stands for, but it's mysterious nonetheless.