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sdodds - I reached out to Lithium Support with the same question and they suggested the following...
You can check the TinyMCE version yourself by going to community > create a post then opening your browser's developer tools -> console -> type "tinymce" and press enter. It will highlight the TinyMCE version.
Once you have the TinyMCE version, you can then go to the TinyMCE changelog page to see the changes associated with each version. Looks like it hasn't been updated in a while so be prepared to scroll through many updates. I hope this helps.