Since 1975, Tamron introduced a new standard for mounting its lenses, which replaced the Adapt-A-Matic mount. Since 1979, a slightly improved design appeared as Adaptall-2. Both are fully compatible and have the same construction, but Adaptall-2 differs in improved Adaptall reliability (said the company Tamron).
Adaptall lenses were all launched in the 1972-78 timeframe, while Adaptall-2 lenses were all launched in the 1982-1996 timeframe. Ability of a lens to use Adaptall vs. Adaptall-2 mount is apparently not straightforward...one person noted, "Adaptall 2 lenses can indicate their maximum aperture to the mount, for fittings which require it. Not all cameras need this information, so some mounts are freely interchangeable between the two types of lens, and some aren't. Confusingly, some mounts are marked "Adaptall 2" when they're also compatible with Adaptall lenses..."
What is the difference between Tamron Adaptall and Adaptall 2 mounts. Are they interchangeable. Could a lens use Adaptall mount, also could use Adaptall 2, and vice versa.