Clamping window and what it protects
The 1.5SMC8.2CAHR7G: The 12.1 V clamping ceiling is what the downstream IC sees during the event — choosing a TVS whose standoff sits comfortably above the rail voltage but whose clamping max stays below the protected device abs-max keeps the clamping element as the sacrificial path and not a load on the line.
Automotive temperature grade and AEC-Q101 meaning
This is the temperature band an engine-compartment ECU or an under-hood module sees — a commercial-grade TVS at 0–70 °C would run out of margin in that environment.