I'm merely asking the questions/posing scenarios.
Again, once you're tested, there's no going back. It's worth a little contemplation...
(Bonus scenario: Ancestry's parent org is bought by a unscrupulous Chinese company outside of Western jurisdiction.)
Your DNA is your unique identifier. Once out there, there's no going back. It's not like closing your Facebook account, changing password etc.
No-one knows what the future holds and how your data might be (mis)used.
But imagine you're mysteriously refused life insurance in the future. Could it...
Does Ancestry give any context with the DNA results? Is it saying you're 90% British/Irish based on, for example, data from the last 1000 years and 1m people?
Edit: I see it says "“a few hundred or even a thousand years ago”.
And this may explain the change in results...
4. What does it mean...
Do you know what Ancestry does with your data?
https://www.cnbc.com/2018/06/16/5-biggest-risks-of-sharing-dna-with-consumer-genetic-testing-companies.html