From the website.....
Custom Staggered SSL-5
complete setup
Calibrated set available with RW/RP middle pickup. Many players use an SSL-5 in the bridge position with vintage output pickups, like SSL-1's, in the neck and middle for tonal versatility.
Custom Flat SSL-6
complete setup
Calibrated set available with RW/RP middle pickup. Many players use an SSL-6 in the bridge position with vintage output pickups, like SSL-2's, in the neck and middle for tonal versatility.
I made sure with my 1st order, the ssl-6, and again with the ssl-5 a few days ago that I was getting the 'bridge' pickup, but there is no 'bridge' pickup. Call Duncan. They are like the quarter pounders meaning no special wind for bridge compared to neck/middle. You can't order an ssl-5b or ssl-6b. I tried. The site is confusing. They must mean calibrated with the middle being RW/RP. That also must me why they suggest ssl-1s and 2s for neck and middle "for tonal versatility".