Sorry, I don't know that much about pickups, I've never built my own... I have no idea why, to answer your question. Can you actually adjust the polepieces on that side? Most pickups with adjustable polepieces only have 1 adjustable coil, so I would think that your pickup should have 2 holders. Are you the first owner of your guitar? The only thing that I can think of is that someone else opened up your pickups and lost the polepiece holder.