Thanks. This seems to check out. I've added it to my thought processes. 12 days to immediate CGT changes. That's not much time to make a decision.
This explains it in a roundabout way:
Held-over gains
Before leaving the UK, it is important to check whether an individual’s switch to becoming non-UK resident/non-UK ordinarily resident will trigger previous CGT liabilities that they have deferred by the use of holdover relief. If you leave the UK within 6 years of receiving a gift that you elected to hold over the gains, a CGT charge could be triggered on the whole of the held over gains.
https://trinityfinancial.ie/leaving-the-uk-capital-gains-tax-implications/
Discussion
I’ll be on a boat in the middle of the Atlantic en-route to St. Kitts & Nevis.
No, I’m not going to have a boating accident, it’s a cruise ship with 5,000 passengers onboard 😂