It's odd that some people still don't understand that Possession is set four thousand years into the future! I know when I first began writing it I entirely forgot to put the year, but once I realized half way through the story of the setting, I put it in the first chapter at the beginning, and I think some just disregard it.
So, yes, Possession and the entire series affiliated with it, is set in the future. Year six thousand and something...I can't remember the exact number. I see a comment someone makes about Harry speaking of his past and them saying it doesn't make sense so many times...I just wanted to clarify. Possession is set in the future. /Way/ in the future.