They don't generally count previews. But if you're being literal as to the number of times the show has been performed, then by all means count the previews. But as for the number of "official" performances, the previews do not count.
"I never had theatre producers run after me. Some people want to make more Broadway shows out of movies. But Elliot and I aren't going to do Batman: The Musical." - Julie Taymor 1999
"TheatreDiva90016 - another good reason to frequent these boards less."<<>>
“I hesitate to give this line of discussion the validation it so desperately craves by perpetuating it, but the light from logic is getting further and further away with your every successive post.” <<>>
-whatever2
It was yesterday's matinee. I was chatting with the conductor a few minutes before the show and he mentioned it was the 100th performance (Hubby won lottery tickets for that performance).