All I know is that Gregg Hopkins and Bill Moore spent a TON of time researching for the book, and both are genuinely good guys. Perhaps I mis-paraphrased the statement: "Removable dollies are included with the cabinets. By 1977, the cabinet no longer has the removeable dollies but has a pair of fixed wheels to tilt the cabinet back while navigating the amp using the new "towel bar." The CTS speakers give way to Eminence drivers around 1972. In 1980, Ampeg designers install new speakers which give the cabinet a power handling rating of 350 watts. This allows the player to use one cabinet instead of two with an SVT head." So what's said is that by 1977, the dollie-style cabs are no longer available. NOT that all cabs are rectangular prior to 1977. My fault.