From looking into it a bit, it looks like each country sets the requirements by themselves. In case of Finland, requirements are documented at least at https://

From looking into it a bit, it looks like each country sets the requirements by themselves. In case of Finland, requirements are documented at least at https://dvv.fi/en/european-citizens-initiative https://dvv.fi/en/european-citizens-initiative ("The organisers must collect the family name, full first names, date of birth, country of permanent residence and nationality for Finnish citizens signing statements of support."). They seem to be also collecting full address when it's not required for Finnish citizens.