Yep. Those are GRAS type standards too, with only basic science behind it.
Fun fact, most welding arcs produce more harsh radiation and UV light than the sun (relatively speaking from distances of encounter, obviously the sun gives out more radiation but that gets filtered) and are built to a higher standard than just a basic ISO 12312-2. It's only the BS sellers that are taking advantage of non-welders by selling them who-knows-what. If they aren't certified for welding, they aren't welding shades, just some crap green tinted glass sold as welding glass. If you use them for actual welding, you might be in for a bigger surprise than using shoddy eye protection to view an eclipse. But NASA only considers 14 as GRAS. 12 and 13 are not. So that is where the lazy science is making runs and pushing bad information.
People who legitimately own shade 12/13/14s for shop work generally do a lot of grinding. Grinding is bright AF and it's funny that you don't come across protective eye wear for grinding on these safe lists. Which is why people who make these blogs with their own researched info but no shop skill are also contributing to some misnomers. They aren't hard to come by, they are just researching the wrong application without knowing any better.
The fact is, there are other layers of protection in place. 100% UV protection and shade 10 might offer different or better protection than shade 12 and 98% UV protection film. But since glasses specifically designed to stare at the sun are not a huge market of research, the quick answer makes its way forward before something with a lot of non-theoretical research. After all, nobody wants to be blamed for making kids blind. Especially not NASA or any municipal agency that hosts events for eclipse viewing.
TL;DR
ISO 12312-2 cardboard glasses are cheap and are just fine
