Regarding Reliant not knowing the difference between Ceti Alpha V and Ceti Alpha VI... it just occured to me that Chekov doesn't think to mention Khan until they get down onto the planet. Sure, it's been 15+ years, but surely if one of humanity's most badass super enhanced villains (who actually brought Earth to its knees) was once stranded on a planet in the Ceti Alpha system, you'd think Chekov would at least tell Captain Terrell and the rest about him. Instead it's like he sees the Botany Bay name and he shits his pants. "Oh fuck, I knew
there was something I'd forgotten about this star system!"
Basically the entire plot hinges on Chekov being a bit of an idiot.