As to disclosing my previous salary? I am virtually positive that I am well paid in my current job, and if I thought proof of this would get me a higher offer at a new job, then I would disclose it. If they asked for proof and I thought it was in my interest to provide it, I would.

In other words, you don't have what we call "morals"? Morals being rules of behavior agreed on by a group of agents for their mutual self-interest. If everyone who believes it's in their interest to disclose former salary does so, management will realize that anyone who doesn't has a low salary and can be lowballed.