They're considered two entirely different things, any theatrical version done of West Side Story follows the same order and dialogue as the 1957 Broadway version.

That sort of goes against the whole point of doing a revival or theater. The beauty of live theater and performance art is the ability to reinterpret the work any number of ways. It's the one art form that doesn't have to stick purely to the source material.

Otherwise we'd get really bored of revivals, really fast.