The history of two-man crime teams aside, Croup and Vandemer are so similar to Pin and Tulip in attitudes, speech patterns, and actions that it's hard for me to see how Pterry created his characters free of Gaiman's influence. Vandemer's obsessive habit of eating any crawling thing becomes Tulip's obsessive habit of trying to consume any inorganic powdery substance as drugs. Both Croup and Pin speak in an artificially "civilized" manner. Croup is literally a consumer of fine art (although Pterry makes Tulip the art expert, which is much funnier). And in the end, Croup trying to save his own life by leap-frogging over Vandemer becomes Pin's murder of his partner to save his own skin.
Pterry may claim that he wasn't influenced by Gaiman, but all of these literary similarities make it hard to believe he wasn't.
Again, that's not actually unique. I mentioned earlier Sabalom Glitz and Dibber. Glitz in particular attempts to speak in an artificially civilised manner, to sound more intelligent than he really is (okay, he's not a complete idiot, and manages to talk his way out of more than a few situations, but he tries to sound more intelligent than he is). To wit, one of his first conversations in The Mysterious Planet
Glitz: Whereas yours is a simple case of sociopathy, Dibber, my malaise is much more complex. A deep-rooted maladjustment, my psychiatrist said, brought on by an infantile inability to come to terms with the more pertinent, concrete aspects of life.
Dibber: That sounds more like an insult than a diagnosis, Mr Glitz.
Glitz: You're right there, my lad. Mind you, I had just attempted to kill him.
In addition, Shlubb and Klump, from Sin City
, make (what I am sure) is their debut in 1996, four years before The Truth
. And they, well, let's just put it this way: they have, as TV Tropes puts it, 'delusions of eloquence'. To wit...
Douglas Klump: The perimeters of our assignment were described to us with specificity, Mr. Shlubb. We are to deposit our cargo into the body of water which we now overlook. It was likeways made clear to us that any embellishments of said perimeters would not be advisory.
Burt Shlubb: I cannot prescribe to such a narrow interpretation of the perimeters which you now invoke, Mr. Klump.
Not that Terry Pratchett would have read any Sin City
graphic novels, but I'm just saying, it's a pretty common type of stock character pairing.