The highest amount of rooms to be updated in one year is eleven rooms, in 2012.
The Beacon, Boiler Room, Iceberg, Lighthouse, Migrator, and Underground Pool received minor updates throughout the game's history, but stayed relatively the same in appearance until the game's closure in 2017. The Boiler Room is the only one of these rooms opened pre-2007 to have never received any update or change in appearance at all.
The Pet Shop has had the most changes of all rooms.
The Stadium is the only room to receive two major renovations; first in 2010, and again in 2014. However, the latter renovation did not include the Ice Rink. Anytime the Ice Rink would return in the winter, it would revert back to the 2010 design.