Re: What didn't I know and when didn't I know it?
Erm this is a SW guideline, so your evidence actually is exactly what Intel, AMD and ARM will use.. the SW didn't use the HW right inspite of guidance since 1971.
If you have ever worked with bare metal and custom ASICs, you'd know this is rather common. One side is blamed, the fence is between HW and SW.
When a workaround exists, SW is at fault. Because the HW people will just say the workaround was always the right method... (you can't use the HW that way you were for performance unless you are willing to take the security risk, we'll improve documentation for next time...)