Consider this a sort of anti-VC Advantage, because it covers cheats that don't exist. If you're reading The VC Advantage and you own (or plan to own) the new VC release of Samurai Shodown, it's probably occurred to you to head over to GameFAQs and look for additional content that can be unlocked. If you've done so, you'd be pleased to find codes to unlock three additional characters.
You'd then be disappointed after trying them, because they're in error. The Shiki and Zankuro unlock codes originate from Samurai Spirits! on the Neo Geo Pocket Color, and the code to unlock the Kuroko judge character is from the Neo Geo Samurai Shodown II. It's easy to understand how the NGPC codes got mixed in: search engines and other automated systems wouldn't be able to tell between Samurai Spirits! and Samurai Spirits (the Japanese title for Shodown), making mixups easy.
You're free to use those saved five minutes however you please!