Documents Not Appearing in Search Results

I recently spent quite some time trying to understand why certain documents would appear in my search results, and others wouldn't.

I looked at the 'Always index all ASPX pages on this site' setting found at Site Settings > Search Visibility. But that didn't resolve the issue.

I looked at the 'Allow items from this document library to appear in search results?' setting found at Document Library Settings > Advanced Settings. But that didn't resolve the issue.

Finally I noticed that documents that appear in the search results have a major version (1.1) and the documents that do not appear, only have a minor version (0.1). So I published one of the documents, did an incremental crawl, and the document began appearing in the search results.

One mystery solved today.