In ArcMap (10.2), I accidentally calculated the wrong field outside of an edit session, so there was no way to reverse my action. I restored a previous version (shadow copy) and joined the tables together using the ObjectID. However, the field calculator was greyed out when I tried to restore that field's data. Why and how do I fix it?
Fundamentals of Field Calculations have a section for troubleshooting why these buttons are greyed out, but these do not fix the problem.