Minecraft version 1.16.5, Fabric
Mod version: moreblocksmod-0.1.6.jar

I tried to give myself stone bricks vertical slab, but when I did /give [username] moreblocksmod:stone_bricks_vertical_slab, it didn't work. Instead, I had to do /give [username] moreblocksmod:stone_bricks_horizontal_slab. Basically it's got the vertical and horizontal mixed up. When I do /give horizontal, it actually gives me a vertical slab.

Actually, I looked in the file and it looks like every single vertical slab is misnamed to horizontal slab. Here's an example of the spruce vertical slabs where the crafting recipe clearly shows it's supposed to be vertical, but the item name says horizontal.

Actually not every single. For example, I notice terracotta bricks are correctly named "vertical" as opposed to "horizontal"

This was an error very very early in the mod, I mixed up the word horizontal when it was supposed to be vertical. Changing the name would result with the blocks being "deleted" (in other words it would be a ghost block) from the world. As of now, I don't have a great way to fix the error without causing a problem for worlds that have this mod loaded. Luckily all the newer vertical slabs have it corrected, as you've discovered 🙂.

Alrighty, understandable! Not a huge issue at all