Stu says that ghosts can become unattached to time... maybe Dresden's ghost is in the past. That would explain why Mort says weird things like, "It’s not enough that you have to keep dragging me into things in life. So now your stupid ghost shows up to do it, too?" The tense of this is all wrong. If ghosts can time travel, Mort would know it, so he wouldn't clue Harry in on it. When did the blizzard hit Chicago during one of the past books? Was it May? If so, maybe that is "when" Harry's ghost is at right now.
There is some really weird discontinuities, though, regarding Mort's house. Harry remembers being killed and saving Maggie and killing Susan BUT he doesn't remember Mort having been bald before or moving to the duplex. So, if Harry is in the past, he remembers "powerful events" like Maggie and Chichen Itza, but doesn't remember things like Mort? That doesn't make much sense.
Unless the stuff about Mort's house and lack of hair is an error, which is unlikely, Harry's ghost is in the past and while he remembers some things about right before he died (Maggie and the offing of the Red Court and his apartment getting burned down), he doesn't remember Mort moving. Nothing else makes sense, but, what I'm saying doesn't make much sense, either!
But if they are in the past, how does Stu know Harry has been dead for 6 months.
This all doesn't make much sense at all. That's about all I can conclude, LOL.