I don't remember ever "missing out" on any parts of the first game
I didn't say anything about "missing out."
I'm sure you had no problem with the game.
But you're not a person who depends on walkthroughs.
What happens in BS1 is that certain paths are blocked off by conversation choices, so you can't do things in the order described in any walkthrough. An option that's closed off may open up later, but not when the walkthrough says it will, and that throws players who depend heavily on walkthroughs.
For example, you have no idea what George will say when you click on a subject. Maybe he will ask another character something useful, but he may also sass the character he's talking to, causing that person to refuse to talk to him any more. The walkthrough is telling you to talk about a certain subject, but because you selected the choice that turned out to be sass, you can't continue talking to the other character and you don't get the response the walkthrough expects. Then the option to go where the walkthrough tells you to doesn't appear on your map. Your only option is to go back to a previous save before George shot himself in the foot with his sassing.
If you're not tied to a walkthrough, you'll eventually figure out another order to do things and eventually get the new area to appear on your map. But if you're someone who depends on walkthroughs, you can easily get stuck, exhausting every possibility you can think of, and no walkthrough can help out.