I am working on adding instrument to my flight instructor certificate, which would mean I will likely take the "Flight Instructor Instrument Airplane (Added Rating)", test Code AIF.
The test for initial CFI with an instrument rating, which is test code FII, "Flight Instructor Instrument Airplane" is 50 questions, but requires no endorsement, however, AIF is only 20 questions and does require an endorsement to take it.
My understanding is that either test would be acceptable to add an instrument rating to a flight instructor certification, giving the applicant the option.
What is the FAA's official logic behind this difference in endorsement requirement?
Here is the testing matrix for reference.