I was part of the original thread. The fact that no part of Hyundai is aware of this certification form is bizarre, but you never end up talking to the right people anyway when you call a phone bank. And it depends on the rep you talk to how far they're willing to go up the chain for you. Via another person who had a similar issue on Facebook, I was able to obtain these certification forms. I attached them in the original thread (which is linked earlier).
Note that this is not likely a Hyundai screw-up, but rather an IRS screw-up. Also note that I never sent in that document (I got it after I already sent my documentation; bill of sale, etc. to the IRS). I received a letter from the IRS earlier this week saying case-closed.
The IRS was probably using the wrong database to verify the VINs when they did their screening, and somehow our cars weren't in there, or weren't qualified as EV's. So the "automatic" letters went out.
I initially also spoke directly with an IRS agent about this, and he was confused as why those letters went out. Without admitting it was their fault, he said to just send them what I had and it should be ok.