Is there a set standard for output displays?

Sometimes there’s a difference between how nbviewer renders output and how it’s rendered in JupyterLab/GitHub. Here’s an example -

Nbviewer Notebook.
GitHub Notebook.

Screenshots below. You can see that nbviewer is being “smarter” and not rendering the progress bar when leave=False. But JupyterLab & GitHub are not following that. Where are these additional rules/logic around output rendering in nbviewer coming from? This is just one example but there could be more like this. Is there any standard around output display that all clients should follow?