Well, the Imperial Guard codex doesn't appear to
have an errata, so I'd say the Codex is correct and up-to-date.
With regards the command squad, it looks like you might actually need one. The codex says that the Heavy Weapons Platoon is a Junior Officer in a Command Squad with one to three support squads. It isn't hugely clear about the difference between Command Squads from the HQ choice and HW Platoons from Heavy Support, but I'm guessing it's just that the HW Platoon is only a Junior officer and they don't want to repeat stats etc.
What points can it not add up?
Checking with a staffer will give you about as close to an official answer as you can get, though. It won't be 100% official, but given that it's their job to understand it all then they should be fairly knowledgeable on a sensible interpretation.