Did corrosion form after I successfully used a bag of rice?

Unfortunately, sometimes it is irreversible and it sounds like you have done pretty much as much as you can. Some say rice shouldn't be used as it can deposit more minerals than just water itself (starch etc.) which can contribute further to corrosion.

Personally with a water damaged device I would tear it down as much as possible and use a combination of Isopropanol 99.9%, time (to dry naturally) and patience, remembering to avoid putting power through any part of the device until you can be fairly certain no moisture remains.