The Related Files drop-down menu doesn’t list all of the files related to my document!
This menu looks at the files related by the saved version of the currently selected document. Try saving the open document and checking the drop-down menu again.
When I click the Browser Preview button, some of my changes don’t translate to the browser!
The browser preview is drawing its source code from the saved version of your document on the hard drive, not the (potentially) unsaved version that is open in the editor. Try saving the currently open document (Cmd+S) and trying the preview again.
Saving regularly is a good habit to have; saving before every browser preview is a must.