https://screenrant.com/oc-biggest-plot-holes-make-no-sense/

The O.C. is one of the most rewatchable prime-time teen soaps, but sometimes it got confusing. Here’s a list of everything that didn’t quite add up.

Hated the Rebecca/Sandy storyline.
I also wonder why Hailey was never mentioned again. I know she moved to her own show, but no mention at all? I would have liked to see her meet Lindsay.
That brings us to Lindsay. I thought it was weird that Kirsten never mentioned her again?
Also, the Kirsten drinking storyline drive me nuts. I don't think it was realistic at all. She knew how Dawn's drinking effected Ryan and I don't buy that she ever would have let herself go there. I think they should have made her addicted to pain killers instead.
I also hate that they had Kirsten walk away from the NG. I would have loved to see her take over after Caleb died. Ryan could have interned with her. Her dating business and the cooking ventures were awful.
Sad about Josh Schwartz. His inexperience gave us the beauty that was S1, but his immaturity ultimately killed the show...plot holes, killing off Caleb, sending off Luke and Anna and then ultimately Killing Marissa. It's like he did away with everything that worked and we were left with an unrecognizable S4. If he would have remain invested, we could have had 5 or 6 seasons. ��