> He asked staff to attend the meeting, which is normally optional.

If I get a note from my boss like that, I consider it mandatory.

But it gets less mandatory the more layers up you go. If I get an email from an SVP that is CC: the entire division saying everyone should go to a meeting I will almost certainly be able to ascertain the contents of that meeting in 10 seconds from someone else who did attend

Surely your boss notices your non-attendance.

If it's actually really mandatory, my manager will probably also relay that directly to me. And that resets the count for "less mandatory the more layers up you go".