You're in the right place, and don't worry about dumb questions.
The fences are 1-Wood, 2-Stone, 3-Iron, 5-Hardwood. If the file you think you are missing is Fence4, it just doesn't exist. (There are several cases where 4 is skipped for some reason!) If you are missing any files, you can always
reset your content files to get them back.
Once you've reset (if needed), you can just unpack once and leave your game folder alone forever after, as replacing files directly in the game folder has
many disadvantages. Using Content Patcher (or JSON Assets, or even JSON Assets + Content Patcher) can get you a straight up replacement without overwriting any files directly, but can also do more, like letting you pretty up your fences
seasonally or only outside. JSON Assets lets you add actual
new fences without replacing the old ones too, which is pretty nice.
Feel free to ask if you have any more questions :)