Article: By the late 1960s, many of the resort's once great hotels were suffering from embarrassing vacancy rates. Most of them were either shut down, converted to cheap apartments, or converted to nursing home facilities by the end of the decade. Prior to and during the advent of legalized gaming, many of these hotels were demolished. The Breakers, the Chelsea, the Brighton, the Shelburne, the Mayflower, the Traymore, and the Marlborough-Blenheim were demolished in the 1970s and 1980s. Of the many pre-casino resorts that bordered the boardwalk, only the Claridge, the Dennis, the Ritz-Carlton, and the Haddon Hall survive to this day as parts of Bally's Atlantic City, a condo complex, and Resorts Atlantic City. The old Ambassador Hotel was purchased by Ramada in 1978 and was gutted to become the Tropicana Casino and Resort Atlantic City, only reusing the steelwork of the original building. Smaller hotels off the boardwalk, such as the Madison also survived.

Question: By what years were many of the great hotels suffering from high vacancy rates?
the late 1960s