Has any voluntary industry code and self regulation EVER worked?
Yes. Good examples can be found the world over: Media advertising standards, financial standards, heck the entire engineering profession is self regulated by its own industry. Many reporting standards are as well. As are quite a few product safety standards (the overall "don't kill people" is law, but how to achieve that is mostly driven by industry self-regulation in many parts of the world).
Now there's plenty of examples where it also didn't work, and those often get followed up with actual laws, but there are still plenty of examples in industry where industry codes self regulated. For example when America shat itself in 2008 Australia was largely insulated from the same problems due to the Australian Banking Association's (industry body) governance code that effectively banned the kind of sub-prime finance dumb-fuckery in the country years earlier.
Want another example? It's not legally required in most of Europe to label vegan products, yet industry has adopted ISO 23662 despite it not being required by any law to do so. And while we're talking about standards, the harmonisation of electrical standards in the EU was almost entirely industry driven, and except for subtleties of specific wiring rules for examples in houses, most electrical standards maintained by CENELEC are entirely voluntary yet followed throughout all industry.