I'm wondering if anyone can help me out with the hallmarks and stamps on an older YG diamonds by the yard necklace? Looking to purchase one pre-loved for my sister, and found one that looks good except the metal purity stamp. My DBTY purchased from the store has AU750 stamped, but this one only has 750. I know the stamps have changed over time, so I'm wondering if anyone can confirm if theirs only has 750 (along with the Tiffany and Peretti stamps)? And if so, around when did you purchase it? Thank you!