The computer system has never moved me from an aisle regular seat to a middle premium seat.

Also, if the OP is an MVPG, keep in mind that MVPGs can self-upgrade to PC on the third day before departure, even if it's more than 72 hours before departure (i.e. this past Friday at about 7:30am, I moved myself and my companion to PC seats for a 10:30am flight Monday), so I always check the seating as soon as I wake up the third day prior to departure.

Even though the website says: "MVP Gold members G, T, R, or W fares 72 hours prior to departure"
https://www.alaskaair.com/content/mi...class-upgrades

....in my experience you can actually start upgrading yourself sooner than that - sometime in the early morning hours of the third day prior.