Take the comic book series Reign of Frogs. In it, it is established that Alan in turned. He becomes a full vampire, we know this for a fact because it is the only thing in Edgar's mostly fabricated story that he is adamant is true. We know that the whole vampires in Washington thing is made up becuase he insists that they're probably real. The coven of dominatrix vampires may or may not have existed, but something did and they attacked it in the daylight. Because we know that, it is likely that he didn't stray too far from the truth when he said that that as where Alan was forced to drink the vampire blood.
In the Tribe there is more stuff about Alan having turned, and no implication at all that he is still a half vampire or that Edgar is in contact with him. He's gone, lost in more ways than one. The alternate ending involving half vampire Sam turning up warning Edgar that Alan is coming for him is my favourite. Alan has turned Sam. If Edgar wants to save his friend, he will have to kill his brother. How delicious. Then there's the ending in which Sam is a full vampire with no explanation as to why. Alan may have been involved there, or not. Either way, Alan is a full vampire, and so is Sam.
In the Thirst, the deck is re-shuffled again. Not only are the Washington vampires now real, but we see Alan turned while fighting them. But he never makes his first kill. He remains a half vampire for five years, eking out an existence carving up animals for their blood and calling it a real life. He had given up on regaining his humanity, and so is lost to Edgar in that way, vampirism serving as a barrier between them that Edgar can't break through, but they are still in touch to the point where Alan isn't particularly surprised when his brother turns up in his house (lair?!) at 1am, and Alan knows where Edgar lives too. And tells him to ring their mum on her birthday, implying he's still in touch with their parents too.
So that's three different realities right there, and to my thinking, the way the franchise treats reality as interchangeable gives fic writers a licence to do the same. If you want Alan to be a vampire, that's canon. A half vampire, ditto. A human? Well, you can set it before he's turned or taking the Thirst as true, after he regains his humanity.
And don't get me started on the other things. Sam's grandfather, was he a half vampire or was that part of Edgar's lies. Something like that can be fit into whatever reality you like. The thing about Sam checking himself into a mental institute is something else that definately happened according to Reign of Frogs, so that can be woven into whatever reality you choose, or not. Is David still alive and searching for Michael and Star? Or was that part of Edgar's lie? The possibilities are pretty much endless, and that equals a lot of fun. Especially when messing with Edgar and Alan...