Seat upgrades!

Hi! I recently discovered you can do seat upgrades. I had done it for all the royals games I attended during the weekday in May. I had purchased a Saturday ticket for the mariners game a few weeks ago, and it wasn’t letting me upgrade the day of. It said none were available. I got nose bleeds and planned to upgrade. Is there certain days and times that they don’t do upgrades? I’m just curious about this 🙂 I have tickets for Thursday and would love to upgrade when I can, but don’t want to risk it being unavailable again.