Robrob,
I believe that the USAF Flight Test Centre at Edwards flew an extensive spin trial after the accidents and did not identify any particular problems with spin recovery. Do you have any details on this trial?
I have heard stories that the early T67s would not recover after 'reverse control recovery' inputs i.e. stick forward before before applying opposite rudder. The recovery from this situation was to re-apply full pro-spin controls and then perform a normal recovery although this invoked a large height loss. I believe that later T67s did not suffer from this problem. Does anyone have any more details of this?