If we encounter the name of what might be a community, our methodology is to add that name to our Gazetteer as a placeholder. As we find more information about that community, it will be added to our Gazetteer.
Just as a reminder: Our definition of a community is rather broad and includes those places (or areas) where several families lived and had a name which identified that place. For example, you might hear somebody say that they are going over to Mile's to see Pete ... Mile's is just a gas station and a couple of homes at the crossroads. While it might not be on the map, everybody in the area knows it by that name.
Places of interest include buildings at a crossroad, several families clustered in a hollow or maybe the location of a way station. It also includes places like mines, lumber camps, ferry crossings, etc. The community might still exist, is now gone or only existed for just a short period of time.
Also keep in mind that Plain could have been on the original document by mistake, misspelled, the original/alternate name of a community that we've listed elsewhere or was placed in the wrong county. Sometimes a post office or train station would have a different name than the community where it's located, so two names might be referring to the same community - we're working to straighten it all out.