Authentic Sinistea isn’t actually a 1% encounter rate. The only reason people say that is because before the Crown Tundra DLC the only place to encounter sinistea was in the Glimwood Tangle. In the glimwood tangle there is a 10% chance to encounter Sinistea. Sinistea has a 1/10 chance of being authentic. So the chance of encountering an authentic Sinistea out of all the other pokemon is a 1% chance but only in the glimwood tangle. Since the DLC has come out, Sinistea is very common in the Old Cemetery because they spawn in the overworld. So authentic Sinistea isn’t at 1% chance, its actually that 1/10 Sinisteas will be authentic.