Carter, Paul A. "The Mystery of the Duplicate Diamonds"
Divergences: 1968 CE, 1972 CE
What if: Robert Kennedy was elected president in 1968 or Watergate was never discovered.
Summary: Two people from different timelines meet at a jewelry store in a third trying to exchange different versions of the same ring.
Published: In Stellar #7 Science-Fiction Stories (ed. Judy-Lynn Del Rey), Ballantine 1981 (0345294734).