the Model X ratings were not released by NHTSA until June 13, 2017 (first delivered X was Sept 2015) and don't think it has been tested by IIHS yet. They generally test more popular vehicles before low volume ones, so we probably will not be waiting that long for the Model 3 test results, but still not likely until the backlog is gone (as both NHTSA and IIHS purchase the test vehicles from dealerships (stores when it comes to Tesla).
IIHS seems to be more interested in the cost of repairs than they are in the safety of the vehicles. I strongly suspect that though the NHTSA tests vehicles at roughly 40-to-45 MPH, that IIHS tests them at higher speeds. Most fatal accidents occur at below 45 MPH on surface streets within two miles of the destination or departed location. If your car is not survivable at 45 MPH, you are certainly dead meat at higher rates of speed when it comes to 'rapid deceleration trauma'. That's why there are no official high speed crash tests.