Your 66 most likely has no blade rub/scratches because the 66 has an extra liner thereby making the only krinked bade the sheepfoot blade.
Probably this, but I think it's also because the pulls on the secondary blades are quite light, which the second run of 66s is notorious for. You can open the blades qith ease. On stiffer pulls you have to use more force, which pushes one blade against another, causing rub. Of course the second liner also helps.
@kamagong I think the 68 buckaroo has a second liner added as well, but I'm not sure.