Michael and Satan's Admin Assistant or whoever she was seemed to have known exactly how they slipped in and out, and they weren't sharing that info. It could have been due to the ferris wheel but I would wager not? The astral projecting also seemed to have gone fine, and while I haven't calculated the probability stats, I'm liable to say that Derleth is just always doomed to be messed up in some way. In fact, that seemed to be one of the main takeaways from the astral projecting to the other timeline; Derleth = doom.
Agreed about the small holes - there have to be. That's likely connected to Julia's network code too, but if anyone would have more info about it, I imagine Rick would.