If the Bird Cage Theatre opened on Christmas day 1881, why does the movie Tombstone show characters at the Bird Cage prior to the October 1881 gunfight?

If the Bird Cage Theatre opened on Christmas day 1881, why does the movie Tombstone show characters at the Bird Cage prior to the October 1881 gunfight? Bob Crabb Seguin, Texas I have seen the opening of the Bird Cage Theatre listed as December 21, December 23 and December 25, 1881. All of them are after the O.K. Corral street fight. I understand why Hollywood uses familiar places like the Bird Cage to juice up the story but the truth is, it wasn’t open at the time of the gun battle.