Think this was me btw so am happy to close. Chilterns  NL are going to expand their extent at some point in the near future (timescale being this decade, probably, I read in their magazine that they need approval from the relevant gov department), so it's going to have to be realigned in full at that point anyway.

some quick links from google if you're interested in this topic:

https://www.gov.uk/government/news/proposals-to-expand-chilterns-area-of-outstanding-natural-beauty

https://www.chilterns.org.uk/what-we-do/future-proofing-the-chilterns/chilterns-aonb-boundary-review/