AyyayYayyayyah! I discovered upon landing from Oaxaca to DF Termnal Two on Aeromexico that CO/UAL is no longer in Terminal Two. They moved 4 days ago. Hary believing this (because I was schlepping 2 big suitcases) a friendly porter came to my rescue, wheeled my luggage to the now defunct CO ticket counter so I could see for myself. Then, he led the way to the AeroTren (monorail)–the only way to get to Twrminal One. This whole process took me about 30 minutes. From the train to the CO/UAL counter wAs another 30 minutes. TG I had time.
Why? Because I first booked round trip RDU to Mexico City, not direct to Oaxaca because I was going to bus from Oaxaca to Puebla. Then I changed my mind and decided to stay in Oaxaca longer. This was an expensive change. Each way from DF to Oaxaca on Aeromexico is $200. Plus they consider this a domestic flight and I had to pay $400 pesos for my second bag each way. Then I needed to retrieve my bags and recheck them passing through security again, then getting them to my carrier.
So, my advice is either stick to your plans, travel lighter than me, and book your ticket all the way through to your destination. Buen Viaje.