Twenty refers to the tarawih units alone. Some reports mentioning twenty-three count twenty tarawih units plus three of witr.
In those reports the numerical difference is a matter of whether witr is included; this explanation should not be assumed to resolve every historical variation.
Opening interactive controls...
Qiyam Ramadan: Tarawih, Qur’an Recitation, and Witr Congregation
Twenty refers to the tarawih units alone. Some reports mentioning twenty-three count twenty tarawih units plus three of witr.
In those reports the numerical difference is a matter of whether witr is included; this explanation should not be assumed to resolve every historical variation.