Sorry, you are right. I was confusing the B66 with the B68.

Here is the Brooks line up as I know it:

B66 = double rails + springs
B67 = single rail + springs
B68 = single rail, no springs
B72 = double rail + loop springs
B73 = B66 with third spring under the nose
B135 = double rail + double springs + nose coil (second most comfortable I've owned, good work saddle)
^^^
All have the same top, which is flatter and wider than the B17 top and has a textured surface, these are for an upright riding position.

B17 = no springs, single rail
Champion Flyer = B17 top + springs, single rail (my favorite, A Champ Flyer Imperial would be the bee's knees)
B66 Champion = Double rail Champ Flyer
Brooks Imperial = B17 top with cutout, no springs, single rail (no numbness, very nice, I may butcher some of my other saddles after owning this one)
B17N = slightly more narrow top
B17S = slightly shorter nose
^^^
These are for a more aggressive riding position, the surface of the top is smooth.

B33 = wider top than the B66-67-68-etc. + triple rail + springs and nose coil, heaviest duty of the Brooks (most comfortable Brooks I've owned)
B190 = widest of the Brooks tops + double rails + double springs and nose coil
^^^
These two are work saddles, bolt upright riding only, textured surface.

Brooks Swallow and Brooks Swift are racing saddles, basically the same top, the Swift has side skirts, the Swallow has tucked skirts.