This goes along with the 2013 WT that changed the definition of the FDSL. There would be a period where the anointed were not discernible because the "enemy" was sowing weeds and they were allowed to grow together with the wheat.
4 Speaking about the wheat and the weeds, Jesus said: “Let both grow together until the harvest.” This command reveals that from the first century until today, there have always been some anointed wheatlike Christians on earth. That conclusion is confirmed by what Jesus later told his disciples: “I am with you all the days until the conclusion of the system of things.” (Matt. 28:20) So anointed Christians would be protected by Jesus all the days leading up to the time of the end. However, since they were overgrown by weedlike Christians, we do not know for certain who belonged to the wheat class during that long period of time. However, some decades before the start of the harvest season, the wheat class became discernible. How did that come about?
So no FDSL during that time. They needed a way to explain this because they have never been able to prove that the FDSL continued in succession after the apostles died.