What is the Accessible Name of a Table Header?

Various attempts at getting a table header to annouce anything more than its visible text.

Goal: Get screen readers to announce more context in header cells for non-visual users — and do so in a repeatable, consistent way across browser/screen reader combinations.

All headers use scope (which overall we have found to do nothing at all in almost all circumstances):

Column One uses title attribute in the th tag
Column Two uses aria-label attribute in the th tag
Column Three uses abbr attribute in the th tag
Column Four uses abbr tag with title attribute wrapping text in the th cell
Column Five uses abbr tag with aria-label wrapping text in the th cell
Column Six uses a span marked as visually hidden but screen reader accessible in the th cell

Testing a Variety of Means for Non-Visual Text in Header Cells
Header One Using Title	Header Two Using ARIA-Label	Header Three Using Abbr	Header Four Using Abbr Tag with Title	Header Five Using Abbr Tag with ARIA-Label	Header Six Using Visually Hidden Text extra text for column six
row two, column one	row two, column two	row two, column three	row two, column four	row two, column five	row two, column six
row three, column one	row three, column two	row three, column three	row three, column four	row three, column five	row three, column six

Screen Reader Testing Results Synopsis

Spoiler alert: Basically nothing you would think works actually works in a consistent way across browsers/AT.

JAWS + IE11: In th cells, only the visible text is announced. In body cells, column three, with the abbr attribute in the header cell becomes the header text for the body cell.
JAWS + Chrome: In th cells, only the visible text is announced. In body cells, aria-label headers are announced, along with the abbr attribute technique of column three.
NVDA + Firefox: The only non-visual approach that works is the off-screen/accessible text approach. No aria-label or abbr technique has an affect.
MacOS VoiceOver + Safari: In th cells, title and aria-label text is announced along with the visual text, and column five's structure oddly reports as a “group.” When in the body cells, only the non-visual text is read, except in column six, where we hear both visual and non-visual text header.
Android Talkback + Chrome: In th cells, aria-label techniques and abbr tag with title attribute all override visual text. In body cells, aria-label headers announce the label; however, the column header with the abbr tag with title attribute is silent and you hear only the visible text.
iOS VoiceOver + Safari: In th cells, only visible text is read. In body cells, only visible text is read (including for column 6).

Conclusion with latest tech, as of February 2018: Only relatively safe approach is the kludge of off-screen accessible text (and even it doesn't work fully with VO in iOS). For the future, an aria-label-based approach seems the most likely to gain traction, unless wider support for the abbr attribute in header cells becomes available.