Battery Terminal Corrosion

My used 2012 Nissan Altima would not start. Purchased it two months prior. All dash lights were on & an alert was beeping. The detail report said that a door was not properly closed. Closed all doors and tried to start again. Headlights functioned properly. Power door locks and trunk release did not work. Could not turn off dash lights or silence the alarm beeping. Called tow back to the dealership. They said that the battery was dead and +post corroded but was good enough two months ago when they inspected it. Can a battery post completely corrode in 2 months? What else could have been wrong?