Your surmise is correct to an extent. Let me try to explain....
The thing to understand and that many miss is that the non-deformation upon the application of 800 Klb longitudinal static force applied to the entire car body in the past.
What has changed is that the car is seen as a structure consisting of two distinct components in the new standard. It consist of an outer car body, which now is allowed to deform into the crumple zone, and an inner safety cage which is not allowed to deform. Passenger occupancy must be limited to the inner safety cage.
The Talgos have the passenger safety cage that does not deform, as was amply demonstrated, but the car body does deform, hence it was not compliant with the old standard but a new train built similarly would comply with the Tier III standard.
The same 800,000 lb test has to be applied to the new cars to verify that the safety cage does not deform. In a well built car (like the Ventures) a static force of 800,000lb won't cause the outer car body to crumple either, and hence by default it will pass. The crumple zones come into play when there is a high energy collision when there is more energy that needs absorbing than in a static test. In that situation, these cars will deform in a predictable way while preserving the passenger safety cage, and not fold up like the Amfleet II Lounge did in the Silver Star. The energy will be absorbed instead into the crumple zone keeping the rest of the car safe.
I don't know if all that makes sense. If not let me know, and I will try again.