Checking Site Map

If you check your sitemap on gatsby with the carbon theme, and do not see your MD files listed. For instance, you could check

You can verify that your MD files are included in the build using gatsby repl

npm install 
gatsby build 
gatsby repl 

Once gatsby repl is launched, you can type pages and verify that you md files are linked. If the MD files are not there, check your gatsby-config.js.

      resolve : 'gatsby-theme-carbon', 
      options : { 
        mdxExtensions: ['.mdx', '.md'],
        titleType: 'append',
        isSearchEnabled: false,
        repository: {
          baseUrl: '',
          subDirectory: '/docs',
          branch: 'master',
        display: 'browser',

This most likely means the mdxExtensions should have included .md. Note, in prior versions I had md without the period, and it was important to include it.