And I forgot to add that the reason only a single 1/3rd disk section was considered was based on experience both before and after the Concorde program. Naturally if a disk breaks into three equal pieces it leaves a mathematical shortfall.for the other two segments. However the predicted generation of three equal pieces (see above) says that they will leave simultaneously so only one is expected to be aimed at the critical parts of an aircraft (critical is in the eyes of the manufacturer and the FAA)
Lessons learned have now taught us that not every 1/3 section has infinite penetration power. In fan disk failures those 20-30lb fan blade fragments tend to cover a lot more area. Thus don't expect to meet a 1/20 safety rate unless you really can shield against. those fragments. The good news is that most really large engines use Kevlar which has been shown to capture multiple blades from a fan disk fracture.
Somewhere on my hard drive I have all this stuff as it was developed for the FAA to review. In the end they went for the subjective stuff because it gave them something to hide behind