I didn't get a specific invite either - but am fairly 'small potatoes' as regards numbers of shares held (sizable by my standards,.... but many would likely not agree with my assessment), and wouldn't have been able to attend anyway as the drive from the DC area and need to take the day or more off with short notice would have been prohibitive for me.
Am guessing that I wasn't on anybody's lists as a 'special guest' either as I am also not in regular contact with the Principles.