Yeah, I agree we can't know for sure. But I think Paul Allen being seen in London can be explained by maybe it wasn't actually Paul Allen - mistaken identities were a common theme among Bateman's peers. Even Paul Allen mistook Bateman as Marcus Halberstram the whole night they were together.

As for the bodies in the closet, I always thought the lady showing the apartment acted very strangely - asking Bateman to leave so there wouldn't be any trouble - as if all she cared about was selling the apartment, and maybe cleaned up the bodies herself so that they wouldn't get in the way of her sale.