Oh, yes, good point, I think you're right about that.
Once upon a time, saddles came with a clamp to hold it to a 7/8" seat pillar, and I think the B66 Champion dates to that time. Now seat posts with integrated clamp are pretty much standard, so two-railed saddles gradually become an anachronism.
I actually knew the answer to my own question since I have one. I just didn't want to come right out and say you're wrong. I will say you are wrong about the 7/8" saddle clamps. All Brooks saddles still come with them. Two and three-railed saddles are still being sold and can be mounted to posts with an integrated clamp with a Joe Breeze Seat Sandwich.