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You can add you KTN without adding your AA FFN.
I stand corrected. Not sure why you didnt say that from the get go as im sure you were just waiting for someone to answer in the manner that i did.
I guess in summary there is a way to get each item accomplished in many different manners.
Personally, i find it easiest to just add my AA FFN to the reservation via finnair (defunct) or Qatar. Doing so adds my KTN as well as my status which enables me to get free bags, better seats, standby on earlier flights etc.
ETA- when i first got GE about 5 years ago, the system was VERY picky about the names matching exactly. By linking the reservation with your AA FFN, it somehow added my full name (including middle name which was not on the original reservations) to the reservation and enabled precheck. In the 6-8 flights ive taken each month in the last 5 years, i missed precheck twice.