david weaver
Larry, I realize you have a lot of skin in this, but I think it's just as big of a reach to not assume that the appearance of a second iron has an awful lot (or everything) to do with mitigating surface quality issues.

I haven't seen any double iron planes that old that look fresh and clean that i could tell what they might've been set up like. But even at 45 degrees, they are plenty functional.

I just can't see any reason why the maker's would've gone to the expense of creating an entirely separate second iron, drilling and tapping it, putting a threaded nut in it and slotting the iron. The only reason I could think of that someone would really do that, especially when it makes it less easy to get a plane to feed, is because it did something superior to the surface of the wood.

While it's not easy to find some literature where someone says "we created the double iron and here's exactly why - to control tearout", I can't see anything that professes superiority of single iron planes, either. You can only guess then why they almost completely replaced single iron planes with the exception of economy lines where price was king.

But I know this much about a bailey bench plane, there is nowhere that I can find a piece of wood in my shop that my much more expensive steeper pitch plane can outdo it, and in most cases I can't get the steeper pitch plane to match the results.

Regardless of the details, if a single plane can do all for someone stepping into the hobby, then that's just more money for tools they'll need a lot more later than they'd need 5 smoothers and 3 jointers, etc.