They've always called me by name or they've said "All standbys will get on - please come retrieve your boarding passes."
Usually it's a very last-minute thing, so I can understand that "I don't want to be a pest" feeling... You are just hanging out there, itching to ask them but not wanting to be so annoying that they "lose" your boarding pass.
Perhaps the agent made some announcement about standbys that you didn't hear?