I have noticed an issue with some of the autotile sets where the:

1. The preview tile does not match what is placed for a single tile; and

2. Some of the single tiles are also not autotiled seamlessly (for example, the top-left grass tile)

I believe this is due to the 24x24 grid not quite lining up correctly. If the autotile set is broken into a 24x24 grid, then a single tile is drawn using each corner of that grid. And in this case, that means any autotile set without seamless corners will also not look correct when used in a single tile, or when a single tile is sticking out from a block of terrain.

(It may not be obvious, but the top-left tile is only a preview for the editor and does not actually ever get drawn in RPG Maker.)

Here is the details of it, which helped me determine the exact issue, in case you haven't seen it before: https://www.rpgmakerweb.com/blog/classic-tutorial-how-autotiles-work

This is not a critical error, as most of these sets still overall draw fine. But I wanted to let you know for future sets or if these can be corrected at some point.

Sorry if some of what I am sharing you already know, I assume you do know and maybe missed these but wanted to share what I found out in case it helps.