Out of the seven times I've seen, six times there's been at least one understudy.
First time: Michelle Aravena as Diana.
Second time: Nadine Isenegger as Cassie & Michelle Aravena as Connie.
Third time: Nadine Isenegger as Cassie, David Baum as Bobby & Jessica Lea Patty as Judy.
Fourth time: David Baum as Bobby, Lyndy Franklin as Bebe & Joey Dudding as Paul.
Fifth time: none; but since it was a Sunday Jessica Lea Patty played Cassie.
Sixth time: E. Clayton Cornelious as Richie.
Seventh time: Joey Dudding as Paul.
A Chorus Line revival played its final Broadway performance on August 17, 2008. The tour played its final performance on August 21, 2011. A new non-equity tour started in October 2012 played its final performance on March 23, 2013. Another non-equity tour launched on January 20, 2018. The tour ended its US run in Kansas City and then toured throughout Japan August & September 2018.