Okay fair, that makes sense. But then, why not have the test just say "write down the letters of the alphabet, in order", rather than being tricky. Plenty of very literate people still need to sing the mnemonic song in order to recall the order.

Oh wait, no, the being tricky is testing to see if people are literate enough to understand the fiddly details of the question. Still, I'd say testing that separately from alphabet skills is more efficient etc.