The good folks at C&G replied to me today, but I'm not any wiser (a tough ask, I know) :Good question !
I'm saving my pennies at present and this is an interesting turn of events. 2394/5 and 2391-52 are all level 3, so it will be interesting to see who will be the daddy ...
Edit : I've just emailed C&G for their advice
"I have reviewed your query regarding the 2391-52 qualification and believe some further investigation is required from our support teams."
I'll keep you posted