Do 'finger' and 'pinky' always show all users currently logged in?

I've been playing around on my university's system and I noticed that sometimes the lists of logged in users I get from finger and pinky appear incomplete. For one thing, there were times when a friend sitting right next to me was logged in but I couldn't find them on the list. I checked to make sure and they were on the same exact computer (remote#) as me. Then there is the results of top. Sometimes it shows programs being run by users, but those users are nowhere to be found on the pinky list. Is there some exception where users can be logged in but not show up in pinky?