I think EI treatment was for those that passed the test. Everyone else that failed the Aero test would have been given the Proto test as part of the Aero test, weeding out the failures as well.
Like your SATs in HS. Failed it meant your college app was most likely denied, but you could still graduate to become a fry cook. But those that pass-fail, with a meh score, could still goto a community college and still apply. But failing that, there is always the fry cook position available.
In other words, you're taking the Aero test and the Proto test, in simulation. Passing the Proto would allow you the EI treatment to compensate for the Protomech's drawbacks, ie: the chemical treatments.
If you pass, congrats.
If not, well the Tech Caste program is ready to except their newest member, here's your hydro-spanner and there's the door, quiaff?
TT