I defer to your superior judgment, m'lord. *Vader kneel*

...oh non. Ils sont les Spartans. Et ils nous regarderont comme des Hilotes ou comme des ennemis."

(Where are we? And... oh no. They are the Spartans. And they'll see us as Helots or as enemies.)

Then 300 definitely got it right; the Arcadians left before the big Last Stand.

Of course, they got other bits wrong, like I said, but the Arcadian bit was pretty much right.

... intended to be historically accurate.

I might be jumping the gun here or making a fu over an implied obvious fact, but both 300 and the original film that Frank Miller based his comic on, "The 300 Spartans" (1962) were both differing interpretation of the events that took place. Neither were intended to be bang-on accurate about the course of the three day battle, but they get the general facts correct.

Another nitpick I noted within the modern "300" - why aren't the Spartans wearing armour? And wouldn't they dump their cloaks aside (as they would usually get in the way or become entangled mid battle)

Once again, this is down to the original creator's take on the battle, but it did kind of not make any initial sense that Spartan hoplites would be charging about with minimal protection.

But, that's just my opinion.

Presumably you'd accept the depicted versions as some kind of alternate-universe canon; I know that's how one would handle a Stargate work, so I figure it's the same deal here.