Tax basis of stock held in joint tenancy
I am trying to establish the tax basis of common stock owned by my aunt. Her parents originally bought the shares in the 1960's. After the death of my aunt's father, the shares were retitled in the name of my aunt and her mother in joint tenancy (WROS). Now that my aunt's mother has died, my aunt is the sole owner of the shares.
What is the tax basis of these shares and what date or dates are important in terms of establishing their value?