The answer
Studies use different outcomes: regret, stopping hormones, changing identity, reversing a social transition, or seeking care for complications. They also differ in age, treatment, follow-up, and loss to follow-up.
Older surgical cohorts cannot answer what will happen to the much larger, younger, and clinically different population treated in recent years. A one-percent talking point should not be used to erase detransitioners or bypass long-term follow-up.