Nichiren's formula to determine how and when to utilize the shakubuku method: The closer the religion or philosophy is to the truth [The Three Treasures and the Three Great Secret Laws], without actually being the truth; and the more attached an individual practitioner or group is to the nearly true religion or philosophy, the more forcefully the shakubuku method should be employed.
The schism between the SGI and the Nichiren Shoshu and, in general, the "war" between the various Nichiren sects is, at least, partially due to the various sects attempting to put Nichiren's formula into practice. None have been very effective because their respective faiths are warped.
From our perspective, the Nichiren Shu is even more evil than the Soka Gakkai because it is closer to the truth without actually being the truth. It is also more difficult to refute. Our refutation of the Soka Gakkai is analogous to Nichiren Daishonin's refutation of the Nembutsu and our refutation of the Nichiren Shu is analogous to Nichiren's earlier incompletely developed refutation of Shingon and Mikkyo [Tendai].
Care must be taken because one or another of the Nichiren sects more or less perfectly embrace and embodies the truth of the Law. For example, Nichiren Shoshu's exclusive faith, practice and liberal use of the shakubuku method is closer to the truth than the Nichiren Shu's while the Nichiren Shu's faith in Shakyamuni mirrors, at least superficially, Nichiren's.
My overriding concern is not numbers but in finding one or two believers willing to adopt the same faith, practice, and manner as Nichiren in order that the Law long endure and prosper.