Stated more succinctly: Any mirror we launch couldn't catch up with any light emitted from before the mirror launched. So we couldn't see our past that way. W

Stated more succinctly: Any mirror we launch couldn't catch up with any light emitted from before the mirror launched. So we couldn't see our past that way. We could do it only with a reflector/bender that already existed in the light cone future from when the light was emitted.