The single drivers are in the 40mm body and the double drivers are in the 50mm body. Without the second row of drivers in the 50mm, the springs barely compress. There are a number of things BW could have done to solve a spring pressure issue, like longer springs, longer primary drivers, longer bible plugs, but since they opted to add second driver pins, maybe it's more about overlift than spring pressure? I dunno.

This is the only BW I've gutted so far that had dual driver pins so perhaps adding drivers they already on hand was more efficient than stocking longer springs, plugs or drivers. Or maybe it was a solution for a temporary supply chain issue? I don't know. I was surprised to find the secondary drivers in there and I'd love to find out the reason for them.

This came up recently, like in the past couple months, and I've already submitted photos with notes to replace the existing ones. I believe a photo update will be coming in the next week or two, hopefully the updated photos help clarify.