Old guy here "USAS Y14.5-66" is short for: "United States of America Standard Y14.5-66". This was a publication of the American Society of Mechanical Engineers which was just a repackaging of ANSI Y14.5-1966.
Most folks back then referenced ANSI Y14.5-1966, eventually ASME gained traction with the dimensioning and tolerancing folks and ASME began publishing the GD&T standards, starting officially in 1994.
The working groups in ASME, SME, ANSI, etc. who develop and publish standards are volunteers. Most are recognized knowledge holders who have the time and support to contribute. Some are not that knowledgeable but sell training, consulting services or ? and are seeking credibility.
Here's all the dimensioning and tolerancing standards
ASME Y14.5-2018, Dimensioning and Tolerancing
ASME Y14.5-2018, Dimensioning and Tolerancing.
ASME Y14.5.M-1994, Dimensioning and Tolerancing
ANSI Y14.5M-1982, Dimensioning and Tolerancing
ANSI Y14.5M-1973, Dimensioning and Tolerancing
ANSI Y14.5M-1966, Dimensioning and Tolerancing