Thanks for your explanation. Just a couple more questions to follow up on though.

I rang BA reservations and asked them to change the number on my booking and they said the MA number didn't match (whatever that means.) I have though, recently made another booking CDG-LHR on ba.com and entered my MA number. It instantly allowed me to select my seat (which I assume means it recognises the Emerald status) and the itinerary directs me to the AC in CDG, again which I assume means the Emerald status is recognised.

Therefore, if I can get BA to update my booking to include my MA number *before* checking in then I assume once I OLCI the status should be on the BP?

That seems like quite a ramble. I hope it makes sense...