I don't think the production has ever hid the fact that the role of Christopher has an alternate. It's been mentioned in all of the press releases, and Taylor Trensch is given equal billing with Alex Sharp on the posters outside the theatre and the title page within the playbill. As consumers, it's as much our responsibility to ask.
That said, I'm rather surprised that the alternate has such a heavy schedule. Is the role really that demanding? Especially for a young performer in the prime of his health and career?
"You travel alone because other people are only there to remind you how much that hook hurts that we all bit down on. Wait for that one day we can bite free and get back out there in space where we belong, sail back over water, over skies, into space, the hook finally out of our mouths and we wander back out there in space spawning to other planets never to return hurrah to earth and we'll look back and can't even see these lives here anymore. Only the taste of blood to remind us we ever existed. The earth is small. We're gone. We're dead. We're safe."
-John Guare, Landscape of the Body