Yes, there are, but since the maximum value is so low, there is little point in doing forensic testing to find out - they are worth £5 to £15 if new, and twice that if fairly old. Utterly not worth doing an isotopic analysis to find out if it was fired 2 years ago by cow dung or 150 years ago by cow dung.
Also, if these locks are so rare and treasured that he and his family looked after them for 300 years, why is he suddenly selling them to you?