Good info that occasional travelers would have difficulty finding!
This itenerary will require a change in MEX and the flight MEX to CTM will be on MexicanaClick. Mexicana reservations theoretically include OP's or "other providers" but it would seem they tend to sell only Click flights if they fly the route. FYI: Aviacsa flys from TIJ to MEX (via GDL) and CTM, sometimes has lower fares, and you can call them directly (1-800-246-0961 from the USA). Also, MX will tell you that you need two hours to connect in MEX, but that's for international to international or international to domestic. Domestic to domestic flights usually arrive and depart Terminal One and an hour is more than enough time even with checked luggage. The daily Aviacsa departure, CTM-MEX *does* connect to Tijuana flights the same day if you/he want to check availability..
Aviacsa discontinued IAH flights but LAS is still on the route map. It looks like LAS is non-scheduled or seasonal service, do you know what's up with that?