I think this touches on the issue of the definition of "truth". A society designates something to be "true" when the majority of people in that society believe something to be true.
Using the techniques outlined in this paper, we could regulate AIs so that they only tell us things we define as "true". At the same time, a 16th century society using these same techniques would end up with an AI that tells them to use leeches to cure their fevers.
What is actually being regulated isn't "truthfulness", but "accepted by the majority-ness".
This works well for things we're very confident about (mathematical truths, basic observations), but begins to fall apart once we reach even slightly controversial topics. This is exasperated by the fact that even seemingly simple issues are often actually quite controversial (astrology, flat earth, etc.).
This is where the "multiple regulatory bodies" part comes in. If we have a regulatory body that says "X, Y, and Z are true" and the AI passes their test, you know the AI will give you answers in line with that regulatory body's beliefs.
There could be regulatory bodies covering the whole spectrum of human beliefs, giving you a precise measure of where any particular AI falls within that spectrum.