Here is a case study from Greece in the ‘20’s, but all you need to do is google ‘ethnic cleansing’ and dig in, and you’ll see government data sources (including census data) all played a part.

[https://ieeexplore.ieee.org/document/11208589]

“The census was conducted in a period of successive wars and rapid territorial expansion. We focus on the handling of the census data for Macedonia, a newly annexed territory that would soon become the site of the first instance of large-scale ethnic cleansing in modern Europe.”