After examining the SEDE documentation, poking around with a few queries, and reading How do you cross the 3k character limit for About Me?, I learned that the Markdown for questions and answers are only stored in their revision history, and that the
Posts table actually contains the rendered HTML from the Markdown, which is why it appears that some posts in the table pass the 30,000 character soft-limit.
According to Jeremy, the About Me sections of user profiles also only contains rendered HTML, not Markdown,
You cannot enter more than 3000 characters for your About Me. The 3000 character limit works properly, but it applies to the Markdown source you enter for the profile's About Me field. However, the Data Explorer does not use the raw Markdown source, it uses the HTML that this is rendered into.
I was able to confirm this by running a few queries in SEDE.
If the Markdown used in the About Me section of user profiles isn't actually stored in the
AboutMe column in the database, where is it stored then? I didn't see any mention of it in the SEDE documentation...is there a column or table that the devs forgot to document?