Interesting point. HR due diligence usually involves a "background check", which is a euphemism for gathering data which is loosely related or sometimes unrelated to job requirements. Asking for a W-2 costs nothing so background checking services do it routinely.
I had a situation where I was applying for a job while self-employed. For complicated reasons, supplying a W-2 was not an option. In the end, the employer and I both agreed that my current income had nothing to do with the price of tea in China, so they made their offer based on what they were willing to pay. The offer made sense, so I accepted it. Alternatively, if they really wanted to use my current income as the baseline for salary negotiation, there was always the possibility that I would demand a salary commensurate with my best year as a self-employed consultant, or at least the average, at which point the deal falls apart.
I'm not a fan of lying about any part of the job application process. It can lead to all sorts of trouble and I have no reason to do it. So I tell the truth and let the process play out. Unfortunately, not everyone plays by these rules. I know of several people with various issues that would never pass a routine background check, and yet they end up working at some of the largest employers in America! If I use LinkedIn to look up people that I know, sometimes I find fake degrees, inflated job titles, fictional jobs at real companies, and fictional jobs at fictional companies. At first i thought it was hilarious, until I realized that honest job seekers are competing against these people. Even worse, I considered the "verifiability" of my own situation and found some problems. Long after my departure, several of my former employers have merged, downsized, sold, relocated, outsourced, or discontinued their operations. Any document that I produce could easily be drafted in Word or Photoshop -- nobody is in a position to prove or disprove anything. If I provide references, they could just as easily be friends with a script.
Thanks to modern technology, it is now easier to "verify" a fake background than a real one!