In this context, I would first present to you a saying of Hazat Aisha Siddiqa(ra), which is well-known to the scholars. Keep in mind that the White Paper asserts that never in the history of Islam has anyone interpreted La Nabiyya ba‘di in another manner. However, Hazrat Aisha(ra) said:
Say, he (the Holy Prophet) is Khatamun-Nabiyyin, but do not say that there is no Prophet after him. (Ad-Durrul-Manthur, vol. 6, p. 618)
Hazrat Aisha(ra) knew that the Holy Prophet(sa) has used that phrase. But she also understood that his words could be misunderstood. Therefore she made a point to clarify that by saying La Nabiyya ba‘di the Holy Prophet(sa) did not mean that there would be no Prophet after him.