French proofmarks date back to at least 1782. Baron Engelhardt published a series of articles on European proof houses for Gun Digest. Way back inthe Dark ages, someone sent me all of them. After Engelhardt's death, Lee Kennett updated them for Gun Digest back in the 1970's. GunDigest Treasury, edited by John Amber covering all of Engelhardt's original articles plus other GunDigest articles from1945-1960. I don't know of any current single source that covers all the European proof houses including the history of proof in those countries.