Talking of decade-long projects, freeing #PAF. the PostCode Address File must be well into it's second decade. Prompted by a recent update https://takes.jamesomalley.co.uk/p/i-had-a-meeting-with-the-shadow-business (and link to a 9 year old post by @Edent https://shkspr.mobi/blog/2014/11/why-do-we-continue-to-pay-for-open-location-data/)
My own posts from that period : http://sk53-osm.blogspot.com/2013/08/pfafing-about-opening-uk-address-data.html & http://sk53-osm.blogspot.com/2014/09/openstreetmap-at-uk-open-addresses.html.
Ludwig Siegele of @[email protected] did a great write-up too https://www.economist.com/international/2014/09/20/getting-on-the-map (paywall)