-
Here's more info:
https://en.wikipedia.org/wiki/Stolperstein
It's not just in Germany, but everywhere people were from who were murdered. It's ongoing.
I don't know where the data comes from, but the Shoah at least is well-documented and a huge effort has been made, and is likewise probably ongoing, to collect information about the victims. I don't know about the Porajmos, but obviously the "Stolpersteine" are for all the victims--from the above article:
The majority of Stolpersteine commemorate Jewish victims of the Holocaust. Others have been placed for Sinti and Romani people (then also called "gypsies"), homosexuals, the physically or mentally disabled, Jehovah's Witnesses, black people, members of the Communist Party, the Social Democratic Party, and the anti-Nazi Resistance, the Christian opposition (both Protestants and Catholics), and Freemasons, along with International Brigade soldiers in the Spanish Civil War, military deserters, conscientious objectors, escape helpers, capitulators, "habitual criminals", looters, and others charged with treason, military disobedience, or undermining the Nazi military, as well as Allied soldiers.
They're called "Stolpersteine", or 'stumbling stones'.