In reply to Justin Tadlock.

Ahhh... so just adding the Gutenberg plugin will actually update the Gutenberg editor with the new features, (that we don't see, because we are using Gutenberg default/cooked-in to WP version). Will try that now. Specifically, we will try: 1. Add Gutenberg plugin to a site already using the built-in Gutenberg editor. 2. Editing posts and pages with the new features (ie: buttons block). 3. Disabling the plugin and seeing what happens... for s&g.