Neverwhere takes place in the London equivalent of the Shibuya underground
Croup and Vandemar were involved in the crucifixion of Saint Andrew.Because if they had crucified anyone, it would most likely have been on a Saint Andrew's Cross. They've been shown to use one, it brought back specific memories, and if it was someone famously crucified on one of them a little less than two millennia before the events of the book, it would most likely have been Saint Andrew.
The Old Firm's last job prior to the monastery commission was catching a wooden golem for a puppetmaster.A fox and a wolf known for making people deliveries and doing murders to people whose last job was in late-medieval Italy? Sound familiar?
Croup and Vandemar are responsible for most if not all of the more unsavoury Reynard and Ysengrin/Isengrim tales.The less unsavoury tales are mostly Bowdlerized versions of their tales and made up from wholecloth, but there may be another, less malicious pair, sort of a set of Reverse Evil Twins.
Richard's still in the Ordeal.Only an angel or God it/him/herself can get through, there is no way for a mortal to pass.
Richard had a nervous breakdown; there is no London Below.He may have had a remission or two, but he's quite mad.
Richard had a nervous breakdown; there is no London Above.Richard's stress of being the Warrior of a subterranean civilization caused him to briefly hallucinate about some sort of crazy, new-fangled city on the surface. Sheer madness.
The Marquis called in Door's big favor in part by teaching him how to Open.Explains the ending, and only the Marquis could keep track of Richard and know about his desire to return because, well he's the Marquis. And the ability is teachable (otherwise how would someone who married into the family walk about the House?), although perhaps not as easy to use or learn for someone without the Talent. Ofcourse this means that Richard now owed him a big favor as well eh? -Not much reason to think it's teachable. Mainly because there's not much reason to think anyone can marry into the family. Mainly because there's no indication that anyone ages in London Below. I suspect that Door's grandfather was the founder of the House of Arch.
Mr Croup and Mr Vandemar are ghouls......Like the ones from The Graveyard Book. The physical descriptions are very similar, as are their diets. Could well just be Mr. Gaiman reusing things, though.
The series takes place in the Old World Of Darkness.The London Underground in it's entirety exists in the Umbra. Door, Hunter and The Marquis de Carabas are Mages, with Door obviously taking several levels in Correspondence. Islington is a Demon, trapped in the Abyss, and Croup and Vandemar are Nephandi serving him. The Velvets are some bizarre, all female bloodline of vampires, or perhaps simply some of the residents of Enoch, which is said to exist in the Umbra.
The series takes place in the New World Of Darkness.Specifically, in something like the Hedge from abletopGame/Changeling: The Lost. Croup and Vandemar are Privateers, Door and the Marquis are Wizened, Lamia and the Velvets are Leechfingers...
Richard is a Finder, or something.Door says that she comes from a family of Openers, and that just happens to be her family's Talent. Richard may very well be from another London Below family, one whose Talent involves finding things. He just stumbles upon Door (literally) and near the end, when he finds the token before the Beast arrives, his description of finding things is a lot like Door's description of opening things. He may have come from London Below, originally, but his family might have sent him to London Above as a young child for some reason.
Anaesthesia knew what fate was coming to her the instant she was told to take Richard to the Market.Even Iliaster tries his darndest to get out of it. Explains why she was so scared about the journey, why she ended up telling Richard her life story. The rats and the Lord Rat-Speaker knew from the start that she was the 'tribute' for Knightsbridge.
London Below is timeless.I'm not even 100% sure that this is a WMG, it might just be canon and I never picked up on it, but considering all of the genre blending, mush of period pieces, and very ambiguous time involved, it feels like London Below is sort of outside time, perhaps a parallel London as opposed to one actually beneath its streets, which would explain things like the Roman soldiers, Croup and Vandemar, Door's anachronistic clothing, and the sort of sense of timelessness, like nobody really belongs in any particular time period.