Apologies if this has been asked -- couldn't find it.

I'm at Boston airport about to board AS15 to SEA. Was #1 on upgrade list but on my way to the airport I noticed they had upgraded #3 and not me or #2 . This was just under 1 hour before the then-posted departure time. At the gate the agent called for me and 3 others, and then processed the upgrades as we went with her.

I've never had my upgrade processed only after confirming I was there -- usually it just updates automatically without being called at the gate -- so I asked the agent why and she said she's only supposed to process them if pax are present, saying she'll otherwise skip them.

Since this isn't my past experience I was wondering, is this true or just an agent making up rules? Seems like an important thing to know. And it's also very annoying as I like to arrive to the gate as close to departure as reasonably possible. Now I have to sit around for a while and then endure Alaska's never-ending boarding process...