Dunno if you're German or Austrian or something, but in Vienna there is a Ziegelmuseum whose curator studies the history of bricks, how they were made and used and whatnot. They have a long list of brick makers in Austria, when they were active and so on.
If you're in another country, they could maybe help get you in contact with a historian local to you.
Could help you learn more about your mystery brick.
I'm in Germany yes, that's a good idea, thank you. The person who sold us the bricks took them out of a building in a village near Karlsruhe, he might know more about the story of that place, we definitely plan on sending him pictures of our construction and we shall ask if he knows more.