I expect that whatever she finds in missing data within the UK public sector, similar or matching examples can be found in other countries, such as here in the Netherlands.
One such Dutch example are the election results per candidate per polling station. The election council (Kiesraad) that certifies election results only needs the aggregated results per municipality, and that is what it keeps track of. Local governments of course have this data immediately after counting the votes, but after providing that data to the Kiesraad their role is finished.
The Open State Foundation (disclosure: I’m its current chairman of the board) in recent years has worked towards ensuring results per polling station are available as open data. In the recent provincial and water authority elections the Minister for the Interior called upon municipalities to publish these results as machine readable data. About 25% complied, the other data files were requested by the Open State Foundation in collaboration with national media to get to a complete data set. This way for the first time, this data now exists as a national data set, and is available to the public.
Viz of all polling station results of the recent elections by the Volkskrant national paper
Added Missing Numbers to my feedreader.