Why the schools disagree
The digital root is additive, so every method of calculating the life path number produces the same base digit. The difference arises only in where along the way a master number gets "noticed". We checked this across all 73,414 dates from 1900–2100: the base digit always matches, but for 20.7% of dates the master-number label differs. That's why we show both variants instead of passing one off as the truth.