In JupyterLab collaborative mode, if a cell output was started in a tab that is now closed, you can still access its output by following these steps:

1. Reopen the Notebook

• Open the same notebook again in JupyterLab. The output of previously executed cells is usually preserved in the notebook file itself, so you should see the output when you reopen it.

2. Check the Kernel State

• If the kernel is still running (check the kernel indicator in the top-right corner), the output should still be visible when you reopen the notebook.
• If the kernel was shut down, you may need to re-run the cell to see the output again.

3. Use the Notebook History

• JupyterLab does not have a built-in "session history" for outputs from closed tabs, but the notebook file itself stores the output of cells. So, simply reopening the notebook should show the output.

4. Collaborative Mode Considerations

• In collaborative mode, if someone else is still connected to the same kernel, the output should remain visible to all collaborators as long as the kernel is active.
• If the kernel was restarted or shut down, the output will only reappear if the cell is re-run.

5. Check the File System

• The notebook file (.ipynb) contains the output data. If you close and reopen the notebook, the output will still be there unless explicitly cleared.

6. Use Version Control

• If you are using version control (like Git), you can check previous versions of the notebook file to retrieve lost outputs.

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Note: JupyterLab does not have a separate "output history" outside the notebook file. The output is tied to the notebook and the kernel state. If the kernel is restarted or the notebook is cleared, the output will be lost unless saved in the notebook file.

If you need to ensure outputs persist, consider:

• Saving the notebook frequently.
• Using %%capture or logging outputs to a file for important results.