So apparently I didn't have to second-guess myself :)
> Nope, May 1999
That's not what you think it is: https://www.w3.org/TR/1999/WAI-WEBCONTENT-19990324/wai-pagea...
The one which the previous version of my site failed to validate is apparently published in 2008: https://www.w3.org/standards/history/WCAG20 and when I wrote those styles back in who knows when [edit: found it, 2014 https://web.archive.org/web/20141219164444/https://egeozcan.... ], I wasn't aware of it. I first said 2001 because I looked at the first draft.
edit: So my 2014 version of the site gets 65, and the current one gets 95 from lighthouse accessibility check with current standards.