Brits being unable to identify the vagina seems like it fits with the innocence depicted in Melody. Other details in there too, although Chef would be proud that they know where to find the clitoris.
Not that everyone in Melody is completely innocent, given the strong presence of girly magazines and nude pictures, even if Daniel having one was completely innocent of any sexual connotations. The boys, especially Ornshaw, weren’t entirely innocent when trying to sneak at least one of them into the girly show. It’s just that they are all still on the edge of childhood and being in love doesn’t make them think “hey, let’s get naked together.” Give them a couple years, if they’re still able to see each other and he still loves her for more than a couple weeks of sixth year.
Of course, given that these days everyone calls the vulva a vagina, maybe it’s not just the Brits who are confused.