I noticed on some event cards have a "if this has been found, do this. Otherwise if you are doing story 1a do this, 1b do this"

The text for the optins have a deeper margin, the last part of the card has a wider margin. Is that last part always done or is that part of the last option?

I read it as written... if they haven't found clue X they all players gain 1 horror (or whatever- thats one I remember), if they have do: Whatever it says for 3B.

You would never do both statements IMO.

No, NEVER do both statements. That's an exclusive or. EITHER deal the Horror, OR follow the specific text.
As far as I know, these events only exist in Story 1. Don't want to spoil myself, so I hadn't looked at the cards.

Why do they either deal 1 Horror (which is boring) or spawn monsters everywhere? Balancing.
If the investigators are faster than the Event counter expects them to be, Zombies spawn to slow them down. Zombies take them 1-2 turns to kill, depending on how good they can evade/one-shot monsters.
If the investigators are slower than expected, they receive 1 Horror but can move on.

I know you don't do both statments. But the way some of the cards are typeset it looks like under the last option that its not part of the option but part of what happens regardless.

Can you give a couple of specific card names and numbers? You don't have to print the text of the card, so you won't spoil anything.

After looking at the cards I noticed the lines between the different events. My bad.