In this section, “will” includes another written instrument of similar import. Unless a will executed on or after June 1, 1947, clearly indicates otherwise, “child”, “descendant”, “heir”, “issue”, or any equivalent term in the will includes an adoptee whether the will was executed before or after a court entered an order for adoption. Unless a will executed on or before May 31, 1947, clearly indicates otherwise, “child”, “descendant”, “heir”, “issue”, or any equivalent term in the will includes an adoptee if, on or after January 1, 1945, a court entered an interlocutory order for adoption or, if none, a final order for adoption.