Most anti-theft tags are not RFID and the gates are not full RFID readers. At least in Europe, vast majority I see are still based on simple resonators that get disabled on checkout. Effectively, the gates only provide a yes/no signal and can't be used for tracking.

Applied Science has a good video on how they work:

https://benkrasnow.blogspot.si/2015/11/how-anti-theft-tags-w...