ExpressJet IATA code before "merger" with Atlantic Southeast? Before 2011, Atlantic Southeast had the IATA 2-letter code "EV". Then,


  On November 22, 2011, both ExpressJet and Atlantic Southeast Airlines achieved a single operating certificate that allowed them to operate as one carrier, using Atlantic Southeast's former call sign "Acey". Effective December 31, 2011, all flights began operating under the name ExpressJet.[7] ExpressJet currently operates as United Airlines Express. 


(so says Wikipedia.)

What IATA code(s) did ExpressJet, or airlines which became ExpressJet, use until that time?
By looking at the Wikipedia article history, one finds that on 8 November 2011 (before the merger), the IATA code for ExpressJet was XE, the ICAO code was BTA and callsign was JET LINK.