Who Brings Potential Outcomes Notation Into Economics?

Heckman and Robb (1985); Angrist and Imbens (1991)

This was written in one sitting. Apologies it’s long but it would take me longer to make it shorter. I’m going to basically say though that the introduction of potential outcomes notation into economics starts in Heckman and Robb (1985) and then is completed in Angrist and Imbens (1991).