The European Seat Back Strength Standard (ECE 17) in many ways is a close cousin to the National Highway Traffic Safety Administration’s Federal Motor Safety Standard (FMVSS) 207 regarding seat strength. The number for strength is so low that no auto manufacturer follows it. The easiest way to describe this is in terms of relative force. The FMVSS standard requires a pull test up to 3300 inch pounds and the European ECE 17 requires a similar test up to a load of 4690 inch pounds.
To put those numbers into perspective, the weakest and most defective production seat on the market today tests out to 8,000 and the typical defective seats that are maiming children, test in the neighborhood of 15,000 to 18,000 inch pounds. If we were to keep inch pounds as the acceptance criteria we would need a seat in the neighborhood of 30,000 inch pounds (or almost 9 times the FMVSS and almost 6.5 times the ECE standard).
Auto manufacturers use the same seat back design and strength in their models sold in both the US and Europe. A good example of how both ECE 17 and FMVSS 207 fail to protect children in rear seats from death and serious injury in front seat back collapse is the recent $124 million verdict in Texas. Eleven-year-old Jesse Rivera, Jr. was left brain damaged in that Texas crash in a 2005 Audi A4 that met ECE 17.
So while the ECE 17 test is higher than the FMVSS test the difference is irrelevant because they are both woefully inadequate. Here is a link reference to ECE 17. The paragraph in question is 6.2 and the reference number that they use is 53 daNm (deca Newton Meters which translates to 4690 inch pounds). https://www.unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/r017r4e.pdf