Originally Posted by akdancer

According to the SEA website, only AS and DL have a dropoff counter within the international arrivals facility (IAF). Link below.
"2. If you're transferring to other airline carriers, exit to the left and recheck your bags at your airline's ticketing counter"
Of course, then another trip through TSA for you, which you would also do if you were able to drop off your bags with AA inside the IAF.

International Arrivals and Passport Control | Port of Seattle