Updated picture:
After some closer inspection, I found out something interesting.
The dark mail in the corner is the untouched voider. The other voider, where it's wider at the bottom, is material I took off my hauberk and used to extend the depth of the voider.
The extended part (not original) is shinier than the rest of the mail. And guess what else? Zero rivets missing. And no rust ... but the original voider has lots of rivets missing, didn't shine up as much, *and* it's already got some rust forming in just hours. The part I added looks like stainless should. The other, just doesn't.
I think I got mild steel voiders instead of stainless. The acid shouldn't have done anything to the stainless except take the coating off, unless I left it overnight or longer. It takes hours and hours of soaking time just to etch stainless with that acid. I've seen people say they soak it overnight to etch stainless. This doesn't seem like it should have happened.
I sent the pics to IceFalcon to see what he thinks. Fingers crossed.