Is there a difference between a strand of Mikimoto pearls bought in 1995 and one bought 60 years ago?

A relative sold my strand of pearls without permission. I went to the jewelry store that he sold them to and found them. The store clerk/owner said no; they had belonged to her mother and were 60 years old. The pearls are 20 inches, 6-5.5 mm pearls and have a yellow gold signature clasp. I have my original receipt from a Mikimoto authorized jewelry store. Is there a way to tell if these are her old pearls or my new pearls.

They really look fresh and have a beautiful luster to them and I do believe they are mine. I have an uneasy feeling about this store, but don't want to call police unless it can be proven the pearls are new. Would the clasp be the same in mine and a 70 year old necklace?