The buffer car protects the entire consist in a collision, not just the tail end car. The issue is not necessarily focussed on rear-ending, the addition of the buffer car is just evidence of a concern. There are many scenarios where extreme forces are possible, not just rearending.
The issue with the Park cars is just the eroded passenger experience in a very pricey first class operation.
There is no absolute "sound", in the sense that any of VIA, the host railways, or Transport Canada may have been the ones to suggest the change in practice. And the adoption of buffer cars must have satisfied their concern, or it wouldn't have been approved as the solution.
To answer your question, there have been all sorts of incidents that relate to this fleet. In 1959, a Park car was demolished in a rear end collision. Eric Gagnon has done a good job of documenting fleet losses,
see here.
- Paul