Is anything required of me if I don't know whether I spent the nights of the Days of Tashreeq in Mina during the Hajj of 2012, due to my ignorance at the time of the obligation to spend the night there?

Staying overnight in Mina is an obligatory rite of Hajj, compensable by sacrifice (dam). However, if you doubt having omitted it after completing your Hajj, nothing is required of you, because doubt after the completion of an act of worship has no effect.