Lyman,
Your quote:
I prefer the TRENT7 pic to the more pedestrian T9drawing
The (GE/Pratt) Engine Alliance GP7200 is a 2 spool engine verses the Trent 900 that is a 3 spool engine. By showing you a cutaway of the GP7200 engine, I wanted you to note only this:
If the stage 2 HPT blade rotor, for whatever reason, moves rearward, disconnected from the shaft, the turbine blades would clash with the stage 1 LPT nozzle airfoils, slowing the disc rotational speed down below that of burst overspeed.
In the Trent 900, if the IP turbine rotor, for whatever reason, moves rearward, disconnected from the shaft, the turbine blades cannot clash with the stage 1 LPT nozzle airfoils to slow the disc rotational speed down below that of burst overspeed.
The difference between the two engines lies in each of their basic designs. The Trent 900 engine is also different from previous (older) Trent designs where blade to nozzle clashing is possible and did occur in several failure instances. So, the Trent 900 is unique in its apparent design and positional relationship between the IP turbine rotor and the LPT stage 1 stator (nozzle). I am not going to speculate as to why the Trent 900 design was developed the way it is.
I don't know how to make this any clearer to you, take your time to understand what is presented, I know it is somewhat complex...