My takeaway here is listing TH as a QB and 3 other QBs on the roster is not a problem because you can have 20 QBs on your roster and still have a QB3 as long as they dont all dress.
But listing TH as a QB and then activating him along with two other QBs will mean that we did activate 3 QBs and therefore wont be able to have an EQB3.
Im not sure that we really care that much about it either way as in an emergency situation whether TH has practiced at QB in the new system or not he may still be asked to take QB reps.