How about the MNA that 'connects' the person or organisation that entered the boat in accordance with RRS 75 with World Sailing?

This seems pretty straightforward. As an Australian boat I would need an AUS. A boat sailed by a Kiwi at a world championship would need NZL. Am I missing something?  We all come from somewhere (unless we are Russian or Belorussian) and that somewhere is our national authority. 

National authority means the member national association (MNA) of their country of citizenship. So, US Sailing for American citizens, RYA for British citizens, and so forth. Here's a list of MNAs by country: https://www.sailing.org/tools/documents/MNAsbyCONTINENT-%5B18903%5D.pdf

Are you asking about cases of dual citizenship? 

Ewan, what are you asking to be interpreted?

What an MNA is and how it is signified is fairly clear in the book? Is it not?

So I assume you want to know which MNA? 

I'd think it's the MNA that applies for Rule 75 - the entry.

Now I know you said no hypotheticals but, I guess hypothetically you could have someone who is a member of a UK club affiliated to the RYA (and would therefore display GBR) but who is also a member of the Spanish MNA (display ESP). I think I may have seen this scenario and I think the sailor may have sailed under two different MNA at two different events. BUT, not saying that was purposely other than which sails he had available!  But I would say a international event where the rule applies should probably ask for the MNA to be specified at the entry?

Thanks for all these comments, very useful. If I may, I’ll add a couple of question for you to have a go at (no hypotheticals): If you live in the same country as your nationality it may seem obvious which Country Code (NMA) you should put on your sail/s - what if you live in a different country to your nationality? My understanding of the relevant WS Regulation is that after being resident in another country you can apply to WS, by writing to the CEO, asking to change ‘…… her national authority ….’ to that country. Seems straight forward.

What about a mixed ‘nationality’ crew? Two SGP crew and two GBR say? Is the ‘nationality based on the majority, the nominated skipper, or the helm?

Or is it based on where the boat is normally located? Do charter boats carry the boats base ‘nationality’ or that of the crew?

Please do comment, with real life examples, then maybe we can draw up a policy as a submission - sorry ‘proposal’ - to WS.