Thanks @mbgower! There was a style guide decision made many years ago by EO (?) that we should use singular. What I do remember clearly is the number of times I was admonished for using the incorrect verb tense. Despite my best efforts, I don't always catch the occasions that I automatically use the plural simply because "Guidelines" ends with an "s".

The abbreviation "WCAG 2.0" reads fine as a singular (where it is easier to think of it as a 'version') but it's certainly a little unintuitive for the spelled out name. I assume the rationale is that it is a single publication/standard. It would be nice to work some nuance into those style guides to handle usage (i.e., spelled out, plural; abbrevation, singular).

RESOLUTION: To use the singular and plural definitions of WCAG 3.0 from the Style Guide