Marker Inbound - the reference is in 61.39
(e) A person is not required to comply with the provisions of paragraph (a)(6) of this section if that person: (1) Holds a foreign pilot license issued by a contracting State to the Convention on International Civil Aviation that authorizes at least the privileges of the pilot certificate sought;
AS Genghis says, it isn't of any real use. I must be the only person ever to use it ... but I did get to use it when I stepped up from a 61.75 to a full private certificate. I emailed the DPE beforehand to check as part of the process. In the end it was a wasted effort as the instructor endorsed me anyway because he figured I was a good bet to pass and would add to his passing percentage. The only real reason to mention it is that it does remove the need to endorse for 3 hrs training in preparation for the checkride. If your TSA training clearance has expired or you have had to change locations for the checkride after the training then it could be a lifesaver.