I was involved in the start up and certification of Dolphin Airways, in Tampa, Fl. back in late 1981. We needed a call sign and I recalled the colorful days of American Airline and their Flagship fleet. We applied for this callsign and it was approved. Dolphin used it through their short life of 1981 to 1984.
In 1985, I was again involved in starting an airline. This time, it was Express Airlines I d/b/a Republic Express in Memphis, Tn and later Minneapolis too. Thinking that the Flagship callsign might still be dormant, we applied to use it and again it was granted.
Republic Express became Northwest Airlink after the Replublic/NWA merger but Express Airlines I remained the certificate holder of this code share regional and the Flagship callsign remained.
Later, NWA acquired and then divested itself of Express Airlines I and the airline became Pinnacle. Although they have changed management and flight crew insignia, the Flagship callsign remains to this day.