Do I have to go to court if I didn't receive a subpoena?

I've received a subpoena twice to testify at a murder trial. The trial was reschedule both times for unknown reasons but this time it's suppose to go on as planned. I received the first two subpoena's about two weeks before the trial was suppose to start but this time I haven't received a subpoena yet and the trial starts tomorrow. I checked the court website but the trial date hasn't been changed. Could this mean that I've been excused as a witness? I talked to someone from the District Attorney's office the second time I received the subpoena and they said that, they had a lot of witnesses that's suppose to testify at the trial. I know very little about what happened other than hearing some gunshots and hearing a car take off. Can someone please help.