The IIHS is always ahead of the curve. They're sponsored by insurance companies, so they have a huge incentive to reduce injuries. (It's amazing what can be done when billionaires have their incentives align with a greater good)

But, they have no power to regulate. Vehicles that do poorly under IIHS testing are completely legal, they simply get named-and-shamed. Sometimes I wonder how lax NHTSA testing would be if it weren't for the comparison point which is the IIHS.

On the other hand, because they're sponsored by car insurance companies, they only care about injuries from impacts.

Like how them changing their whiplash tests caused neck pain and injuries for anyone significantly outside their test dummies. But because they're not caused by an impact, but rather because they fail cars that allow the user to adjust head restraints to be less effective for the median posture, they don't care.

And they don't care about anything else. Dead people don't pay premiums.

Thankfully NHTSA has a much broader mandate.