According to a 2017 study, pain is the most frequently reported symptom of PCOS. Even though pain is not a symptom of PCOS!
The solution to this paradox is that both PCOS and period pain are common, so it’s easy to have both a PCOS diagnosis and period pain (including pain due to endometriosis).
That’s true whether the PCOS diagnosis is valid (i.e., there are symptoms of androgen excess) or invalid (i.e., the diagnosis was mistakenly based on an ultrasound finding).