Nothing to do with irrigation.

Instead, catfacing. That means the tomato was set when temps were on the low side.

Bottom line: Keep it.

Hello, i'm an agricultural Engineer from Colombia (Southamerica) and i've worked with tomato for a few years. Here, catfacing presents in a different way. Normally here, Catfacing appears when irrigation is made in hours when the temperature is high, like between 12:00 PM and 2:30 PM. (This is the tropic, you know...). In all cases the tomatoes present deformities but in almost half of the cases the exposition of placentary tissue does not appear along with the deformities. The exposed placentary tissue, which in my oppinion is what your tomatoes are starting to develope, is associated to Boron deficiency. It would be a good idea buying a microelement mix fertilizer and try it in some plants to see if the problem decreases (It usually works here). About keeping or discarding the fruit? Well, it depends on your goal. For instance, here, people do not buy tomatoes showing that problem, so farmers pull them of the plant as soon as the problem starts to show. That way the energy and nutritional resources consumed by the abnormal tomato can be used in the developement of the healthy ones. But if your goal is home consumption, you can keep them and just discard the affected area before eating. I know our crop conditions are quite different here but i hope that something that i wrote here can help you somehow. (PD. Excuse my grammar, english is quite difficult for me).

It's just aesthetics - it shouldn't affect the taste. I would just leave them, especially since it's a determinate variety, but it's up to you.