Sometimes the mark on the clasp only identifies the company that made the clasp, not the strand of pearls. If the company is big and important, like Mikimoto, or even Honora, they may have custom clasps made just for them. It feels good when you find a reference to the markings, but I suspect many go unidentified.
Please do post photos of your other pearls. This strand appears somewhat off round so based on the size and if the date is correct, they would be akoya from Japan, not Chinese freshwaters.