When creating a Dashboard panel, users can choose to share with other users. Some users find that the dashboards they create and share are not in the list when clicking the Select Shared Dashboards button.
The list of Shared Dashboards only shows a list of those dashboards shared with the user. If a user authors a dashboard and shares it, it will only show under that user's dashboards. If the user would like to know which of their dashboards are shared, click the "Sharing" button or change the naming convention to include "-shared" to the end of it, for example.